Actually yes you are right that happens when you enter the room he is in and when he spots you.

Quote from the wiki page

"Secretly, his former political allies decided to informally exile him there after finding out he was running a child prostitution ring. It’s implied that these same politicians were the ones to hire Agent 47 to kill Delahunt’’

So probably found out that they sent Agent 47 after him. That is why there was so much security around him not only because he was the US ambassador of the Vatican.