This is impossible. There was never a time where the Replit editor didn't capture the tab key (that would be dumb). It must've been something else. Maybe it was a homemade "REPL" the company you were interviewing with made?
I was surprised too! I was sent a link and then it opened the replit site. The window was split vertically and one half it was coder editor. It looked like a "free" version where you can type some code and run it. And every time I hit tab the editor went out of focus.