To be fair it looks like it was posted in r/gimp and we don't know what the OP actually said in the text. In my experience, usually, when something like this happens, they usually heavily criticize something and call it 'garbage' or something similar.

It'd be like going into any passionate community about something and calling it trash, then being 'shocked' that there's a bunch of responses belittling them. This isn't a FOSS specific problem. Go into r/windows or even r/techsupport and trash it while comparing it to anything else like MacOS, Linux, *BSD, whatever and you'll get a bunch of toxic responses. This would also be mostly true of any other non-computer hobbyist communities surrounding a specific brand or product.

When I would see someone ranting "I'd switch to Linux but the community is toxic" in somewhere like PCMasterRace, I'd ask "Can you link to the post?" and if they did it was so common that they straight up trashed Linux in whatever distro community that they posted to that I don't recall a single instance of it simply being "Hey I have this problem. What do I do?" and there being nothing from the OP trashing it in responses or the original post.

I'm not sure if it will become the same as the federated community gains popularity and you have more regular user-type people posting in those niche/passionate/whatever communities more regularly.