* ET was a puppet: The character of ET was primarily controlled by a puppeteer named Pat Welsh, who operated the puppet from inside a costume.
* The "legs" were a costume element: The puppet didn't have actual legs like a human, but the costume had the impression of legs.
* The actor did have legs: Pat Welsh, the puppeteer, obviously had legs, but those were not seen on screen as he operated the puppet from inside.
So, in a way, the answer is "yes" (the actor who operated the puppet had legs), but not in the way you might be thinking!