It has been interpreted as the depiction of a very particular moment in the romantic life of David Hockney. Portrait of an Artist (Pool with Two Figures), which sold for $90.3m (£70.3m) at auction in New York last week, shows his former lover and muse standing beside a pool – and a man who might be the painter’s new boyfriend swimming under water.

But Peter Schlesinger, Hockney’s ex-partner who was one of his students at the University of California, Los Angeles, has rejected the interpretation of the work that has now made the Yorkshire-born painter the world’s most highly valued living artist. He says it is not an “emotional” depiction – and is probably not even, in any meaningful sense, a portrait of him.

“It’s an amazing picture, and it contains his two most iconic genres in one picture, swimming pools and double-portraiture, but I can’t speak to its emotional element because I don’t think it is emotional,” Schlesinger told the Observer. “There’s the figure of me standing and the figure in the water differently painted. It was a conceptual problem. I don’t even think it’s a portrait of me, really.”

Schlesinger, a ceramicist who recently published two acclaimed photography books describing London’s creative milieu of the early 1970s, believes the more elaborate romantic interpretations of the painting could only be made “with hindsight”.

But the interpretations persist, with New York Times critic Roberta Smith describing the painting last year as “a complex, emotion drama inspired by a personal relationship”.

When the 1972 painting went under the hammer at Christie’s, dethroning Jeff Koons as the most expensive living artist, bidding went on for nine minutes, a testament to Hockney’s growing critical and commercial stature.

Christie’s described it as “one of the great masterpieces of the modern era”. The auction house did not disclose the identities of either the buyer or the seller, but it was reported that the painting had belonged to the Bahamas-based British currency trader Joe Lewis, whose company owns Tottenham Hotspur football club. Lewis is believed to have amassed an art collection worth $1bn, including work by Picasso, Matisse, Bacon and Freud.

Hockney, now 81, staged the swimming portraits at the Provençal villa of the filmmaker Tony Richardson, Le Nid du Duc – “the owl’s nest”. But Schlesinger was nowhere near the pool; he posed for the portrait, fully clothed and in London’s Kensington Gardens, while the picture itself was executed during a three-month work binge after the two men broke up.

In the picture, the Schlesinger figure is dressed in a pink jacket overlooking a sun-dappled swimming pool. A range of mountains rises up as a backdrop. The swimmer is thought to be Schlesinger’s new lover, Eric Boman. But Schlesinger just sees it as “a great painting”.

“I didn’t interpret it as a break-up picture,” Schlesinger said. “You can talk all you want about Jeff Koons’s Balloon Dog [a version of which had previously held the record price at auction for a living artist] but there’s five of them around. With David, there’s only one of them, and it’s a great painting.”

Hockney’s break-up with Schlesinger in the early 1970s was chronicled in the 1974 film A Bigger Splash, which takes its title from the artist’s best-known Californian swimming pool picture.

The sale of Portrait of An Artist came as the flow of established masterworks to market slows to a trickle. But when they do come up, the competition is intense.

Days before the sale, Edward Hopper’s 1929 painting Chop Suey sold for $91.9m, with fees, an auction record for the artist. The previous best price for Hopper, set in 2013, was less than half, at $40.5m.

Schlesinger believes Hockney’s moment has finally come: “David has always been a very popular artist but his values weren’t in line with that. Now his prices are catching up with his reputation.”

Hockney’s increasing popularity may in part also be due to an acclaimed 2017 retrospective at Tate Britain and New York’s Metropolitan Museum of Art. The show received praise from Smith of the New York Times for making clear Hockney’s “courageous” representation of homosexual love and comradeship.