> i would be pretty irritated if someone ripped off my idea after working with me
Are you sure he really 'ripped off' anyone in the first place? The first thing I thought of when I read this article was 'that sure seems like the same thing Jupyter was made for'. A quick google shows that Jupyter was a couple years ahead of Repl.it, and I doubt that Jupyter was the first to come up with a web app REPL shell in the first place.