In 1976, DC Comics and Marvel Comics jointly published Superman vs. The Amazing Spider-Man: The Battle of the Century, which was written by Gerry Conway and penciled by Ross Andru, with Neal Adams and John Romita Jr. working on uncredited redraws. The unparalleled endeavor brought the two superhero universes together for the first time in an adventure that saw Peter Parker/Spider-Man and Clark Kent/Superman defeating the combined forces of Doctor Octopus and Lex Luthor.
A spiritual successor to the comic crossover, Jim Shooter, Marv Wolfman and John Buscema's Superman and Spider-Man, released in July 1981. And in that same year, Peter and Clark met each other outside the comics, with the latter appearing in the the Spider-Man animated series.
In Season 1's "Curiosity Killed the Spider-Man," Spider-Man foils thief and occasional love interest Black Cat's plans to rob wealthy guests at the Daily Bugle's New Year's Eve party. After that happens, Black Cat tells Spider-Man she'll steal a priceless artifact -- the Maltese Mouse -- unless he can stop her. Spider-Man then investigates Black Cat's criminal activities at the city's docks and chases a decoy truck she uses to throw him off her scent.
While trying to rush to the docks where Black Cat and the Maltese Mouse really are, Spider-Man stops to call Betty Brant after forgetting about her lunch date. Inside the phone booth is a black-haired man wearing a blue suit and glasses. The man stares at Spider-Man for a moment and then hurries away, with Peter wondering aloud where he's seen him before.
The man Spider-Man encounters in the phone booth is clearly meant to be a reference to Superman, who quite famously used the location to change from a mild-mannered reporter into a superhero for much of his history. Spider-Man commenting on having seen Superman before is almost certainly meant to be a tongue-in-cheek reference to the the two having crossed over in the past, though due to the production time associated with animation, it's unclear if the production team would have known about their 1981 crossover.
This isn't the only reference to Superman in "Curiosity Killed the Cat" either. Later in the episode, Peter asks Betty on a date to see a film about "a strange super guy from another planet who's allergic to green rocks." This is a clear reference to Superman, whose weakness is kryptonite, the most famous variety of which is green. Superman II, the second film with Christopher Reeve playing the Man of Steel, released the same year as "Curiosity Killed the Cat" and is almost certainly the reference here.
The reason this iteration of Superman isn't explicitly identified as such is almost certainly rights issues. There have been a handful of crossovers between Marvel and DC in the comics over the years, as such negotiations are pretty much always difficult to pull off. As such, Spider-Man opts to make a reference to Superman without ever explicitly identifying him as the Man of Steel, though those familiar with the hero would certainly be in the know.