One of the guys wrote something and published it as open source. The other got to use it for free but still complains with an inappropriate tone. Hard not to side with the first one by default.
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".
If someone whines about a perceived shortcoming in stuff which has been released incomplete, but free and modifiable, then they can expect short shrift.