Well they certainly couldn't call it "free software", that involves many more assumptions than "Open Source", and it might not even be free of charge. :) Blame Richard Stallman for using an incredibly common word with many meanings to refer to something that has one incredibly specific meaning which is unintuitive to most people, and to pretty much anyone who isn't a developer.
I think several decades of Open Source boosterism may have eventually given some people the wrong idea about what it's all about. Two annoying trends I've noticed in the last 10 years:
(1) (what this poor guy seems to be running into) People treating Open Source as anything other than charity from the people who put it out there. The people who make it generally don't owe anyone anything, including the people who use their code. I sometimes see very harsh criticism from people within the community that assumes anyone putting anything out there has to accept all sorts of responsibilities: maintaining a community, keeping on top of bug reports, acting as an integrator for people who want to send in patches, making sure that all packaging and documentation conform to some very high bar and/or specification, etc. Just because somebody puts something out there doesn't mean it has to be a second job for them, and doesn't mean that they are obligated to do anything for anyone, including responding to emails or dealing with bug reports or patches. It's perfectly fine to stop maintaining something after a while, or to just throw code over the wall and never touch it again after it's out there.
(2) (not this case) People treating Open Source as some avenue to professional fame or an eventual source of income. Yeah, that can happen, but it very rarely happens, and it's not a good reason to write it in the first place. This is the result of too many people using business arguments as a fundamental justification for doing Open Source, and people saying stuff like they only hire people who have projects on Github, and only if they like what they see. If someone's primary motivation is fame or money, Open Source is a terrible way to accomplish that. It's possible, just highly unlikely, plus I think it's much less likely to happen if that's someone's goal from the outset.