Do you think Rockstar is omniscient?
Seriously. There is actually zero way Rockstar would ever know even if you outright stole some of the code unless you were to admit it. And definitely not if you got some inspiration from it.
The derivative code will get compiled. What are they going to do, pick apart the machine code from every game released from now on to see if it somehow matches a chunk from GTA? And then somehow track down and prove that one of the probably dozens of employees who worked on the game looked at this leaked source code? Good luck with that.
It is the epitome of a solid 7/10 game. Good but not great. There's nothing seriously wrong with it, and I wouldn't say it's a waste of time but also nothing really that great about it.
It feels more like a prototype for a good game than anything especially with how short it is so I have high hopes for the sequel at least.