I think really thinking on why I'm siding with one person almost immediately despite not having much context in this is really revealing and maybe not a little unpleasant.
If someone whines about a perceived shortcoming in stuff which has been released incomplete, but free and modifiable, then they can expect short shrift.
Literally every open source license says something along the lines of "there are probably bugs and stuff; it's not my problem".
I really can't even comprehend this mindset of "unless it'll work for people without issues, don't put it on github".
It might be reasonable for an emoji library to say 'ALPHA: missing a few characters' to stop people from trying to debug non-existent rendering problems - but he puts this in a very aggressive manner.
As you said, they're both wrong (and right) in their own ways.
A Github issue where a user behaves rudely and labours under the misapprehension that he is owed anything by the person who made his work available for free. All that because of a limitation of the underlying library he would likely have found out about if he had bothered doing his homework. It's not very difficult to pick sides here.