I realised that Superman was nicknamed the Man of Steel by American writers, at the same time Stalin, the leader of a country idealogically opposed to the United States had a leader with the same nickname.
Was this commented on by people at the time?
Well, at least it was commented on by people in 1967:
In April 1967, Jim Doody from Altadena, California, wrote to Action Comics (#349) noting that “Stalin” translated to English as “Man of Steel” and warned DC, “Watch it, before the F.B.I. accuses you and your Man of Steel of Communism!” DC replied, “Have no fear! Despite that red cape he wears, anyone can see that Superman is true-blue. And everyone knows that accusing him of being un-American would be an F.B.I.!”
Source: Ian Gordon, Superman: The Persistence of an American Icon, 2017.