So he can move on to focusing on his next game. He added all planned features, so all that is left are some bugs, which don't require full time development.
It is indeed a quirk of the engine, I've seen multiple games with the issue, in fact, I have yet to see one using these assets without the issue. The animations are a different issue altogether and are, as he did admit, his lack of skill. It is done, Beta means it isn't feature complete and is definitely buggy, this game, while buggy as some final form games are, is feature complete. To get the complete tag, he needed to implement everything planned, bugs do not disqualify it from that. There are quite a few games that were added in the last two months alone with the complete tag from the start that have catastrophic bugs, by which I mean the game outright terminates due to a fatal bug, but they are feature complete and the devs of said games have finished development and moved on.