Our daily lives are mostly a mixture of drab routine and unpleasant surprises – however, from time to time, something unexpected happens which makes life worth living. Something of this order occurred at the memorial ceremony for Nelson Mandela last week.

Tens of thousands were listening to world leaders making statements. And then … it happened (or, rather, it was going on for some time before we noticed it). Standing alongside world dignitaries including Barack Obama was a rounded black man in formal attire, an interpreter for the deaf, translating the service into sign language. Those versed in sign language gradually became aware that something strange was going on: the man was a fake; he was making up his own signs; he was flapping his hands around, but there was no meaning in it.

A day later, the official inquiry disclosed that the man, Thamsanqa Jantjie, 34, was a qualified interpreter hired by the African National Congress from his firm South African Interpreters. In an interview with the Johannesburg newspaper the Star, Jantjie put his behaviour down to a sudden attack of schizophrenia, for which he takes medication: he had been hearing voices and hallucinating. "There was nothing I could do. I was alone in a very dangerous situation," he said. "I tried to control myself and not show the world what was going on. I am very sorry. It's the situation I found myself in." Jantjie nonetheless defiantly insisted that he is happy with his performance: "Absolutely! Absolutely. What I have been doing, I think I have been a champion of sign language."

Next day brought a new surprising twist: media reported that Jantjie has been arrested at least five times since the mid-1990s, but he allegedly dodged jail time because he was mentally unfit to stand trial. He was accused of rape, theft, housebreaking and malicious damage to property; his most recent brush with the law occurred in 2003 when he faced murder, attempted murder and kidnapping charges.

Reactions to this weird episode were a mixture of amusement (which was more and more suppressed as undignified) and outrage. There were, of course, security concerns: how was it possible, with all the control measures, for such a person to be in close proximity to world leaders? What lurked behind these concerns was the feeling that Thamsanqa Jantjie's appearance was a kind of miracle – as if he had popped up from nowhere, or from another dimension of reality. This feeling seemed further confirmed by the repeated assurances from deaf organisations that his signs had no meaning, that they corresponded to no existing sign language, as if to quell the suspicion that, maybe, there was some hidden message delivered through his gestures – what if he was signalling to aliens in an unknown language? Jantjie's very appearance seemed to point in this direction: there was no vivacity in his gestures, no traces of being involved in a practical joke – he was going through his gestures with expressionless, almost robotic calm.

Jantjie's performance was not meaningless – precisely because it delivered no particular meaning (the gestures were meaningless), it directly rendered meaning as such – the pretence of meaning. Those of us who hear well and do not understand sign language assumed that his gestures had meaning, although we were not able to understand them. And this brings us to the crux of the matter: are sign language translators for the deaf really meant for those who cannot hear the spoken word? Are they not much more intended for us – it makes us (who can hear) feel good to see the interpreter, giving us a satisfaction that we are doing the right thing, taking care of the underprivileged and hindered.

I remember how, in the first "free" elections in Slovenia in 1990, in a TV broadcast by one of the leftist parties, the politician delivering the message was accompanied by a sign language interpreter (a gentle young woman). We all knew that the true addressees of her translation were not the deaf but we, the ordinary voters: the true message was that the party stood for the marginalised and handicapped.

It was like great charity spectacles which are not really about children with cancer or flood victims, but about making us, the public, aware that we are doing something great, displaying solidarity.

Now we can see why Jantjie's gesticulations generated such an uncanny effect once it became clear that they were meaningless: what he confronted us with was the truth about sign language translations for the deaf – it doesn't really matter if there are any deaf people among the public who need the translation; the translator is there to make us, who do not understand sign language, feel good.

And was this also not the truth about the whole of the Mandela memorial ceremony? All the crocodile tears of the dignitaries were a self-congratulatory exercise, and Jangtjie translated them into what they effectively were: nonsense. What the world leaders were celebrating was the successful postponement of the true crisis which will explode when poor, black South Africans effectively become a collective political agent. They were the Absent One to whom Jantjie was signalling, and his message was: the dignitaries really don't care about you. Through his fake translation, Jantjie rendered palpable the fake of the entire ceremony.

• This article was amended on 16 December 2013 to comply with our editorial guidelines