Although I have no doubt it happened exactly as you claim (based on my own experience in this business), I'd be careful with using sentences like "here are the facts". All you have presented is your version of events. I'm sure the Smule CEO has a version, too.
I was thinking the same thing.
Was it developed on that company laptop though which it sounds like they never got anything in writing to overrule the contract that would have been in place that anything developed on company equipment belongs to the company.
Also a lot of hand waving saying Smule doesn't have anything like Shred then go on to describe Smuush which sounds like a far more basic version of Shred and kinda looks like you decided how to make a "Smuush 2.0" then left and built it without them.
Not to mention don't most contracts have a non-compete claus?
depending on the (hypothetical?) non-compete, building an app similar in concept (even if from scratch) could violate the contract. the author could be completely in the wrong here without a leg to stand on.
Exactly that's why I pointed it out, "Just a standard contract" means it's time to read the f-ing contract before you sign it and keep in mind what it said when you exit.
There is all sorts of things in even "standard" creative industry contracts that can be lethal if you don't pay attention. The fact he accepted that laptop while still half working with them screams to me they didn't read their contracts.
The correct way would be to say "No you can leave the laptop here and I'll come in and work on the handover when you need me, it's not my property and I don't want remote access to your source code"
The part that baffles me, and I'm sure everyone else, is why did he keep the laptop? Why would I want a piece of equipment laying around to do the company a solid and further help them out if I'm gone? If I'm leaving a company I don't want to have anything linking me to them. If they want help, they can get with me on a freelance basis and I'll use my own equipment.