I don't disagree with you that I would also be very annoyed as Onyxdime if he's being honest and the programmer seems incompetent. That doesn't surprise me, as honestly, a lot of adult games are built using dogshit methods. Working on the surface, but could be done much better. Good programmers are working in mainstream industry and being paid extraordinarily well.
That said, alpha testing is meant to catch bugs. Beta testing is when everything should be working, with maybe some occasional errors that shouldn't be game-breaking. It's possible the programmer was able to access the content on his build, but things can go wrong because of several reasons (using versions of RenPy, built in one OS and exported to another, things can go wrong in extraction of compressed files, typos the programmer made by hitting their keyboard or adding something small after already testing a section, among other things).
Some of the errors Onyxdime shared here seemed like really easy fixes, while others I don't really understand at all.