I still haven't played this game, I'm going to download it for the first time now. But one thing I can tell you for sure is that with the right settings webp can offer basically the same level of quality as a png, or at least so close that you wouldn't be able to tell the difference but using only a small part of the space needed by a png of a similar level of quality. I don't know if that's the case with this game since this will be my first time with it (but I think the file is way too small so I'm guessing there's more compression than necessary), but if the developer decided to go with webp from the beginning the game would be smaller, it would probably look the same, and you'd have no idea it's not png unless you saw the files yourself.
Using uncompressed assets for everything not only in this kind of game but in any game is a waste of resources for the user and it doesn't offer any real advantage.