Security through obscurity is generally considered terrible practice in the cybersec community. It's much better to actually find and fix the flaws than just put your head in the sand and hope no one notices the issues.

Exploits in games and the exploits used by hackers for various other purposes are very similar in nature if less often in effect.

Judging by the fact that I have never heard of the game or the company before, I guess it's tiny and obscure, meaning it would have either been completely ignored by hackers or some hacker would completely flatten it with hacks.

Probably nothing about that has hanged by open sourcing it.

Probably, and that's the point, since said exploits can be then publicly acknowledged and patched.