This is correct. Tons and tons of cartoons featuring popular characters have fallen into public domain. That doesn't mean the character itself is PD, just the film.
That's one reason PD cartoon collections always have shit box artwork, they're not allowed to draw the character in an original pose and must use a direct capture of them from the film.
People sometimes think public domain films are all just moldy silent films from the early 1900's. PD films include some Gamera, Godzilla, most of the Warner Bros toon characters.