So other projects are not supposed to critize Google? Graphene's focus is on security and they complain about lack of security in your products. Seems valid to me.
Also security and using non-Google OS are not niche usecases. I'm not sure how you are working on Android, the most popular OS while claiming security is a niche usecase. In fact, I have less confidence in security of your work.
The way I read the comment (admittedly putting words in their mouth), is that there are different ways of "complaining". I am someone who is actually quite sympathetic to Graphene's project and have considered getting one of their Motorola supported phones when they come out. But every time I encounter their writing, they come off as unnecessarily abrasive. They could be making the same points with a lot less potential bridge burning.
They are not neutrally pointing out places where their preferred priorities aren't being met (which would be reasonable), but they are speaking (forgive me the hyperbole) like religious zealots. I don't blame someone who doesn't share their particular viewpoint with being hesitant to work with someone like that.
As a consumer, I don't particularly care. I'm not going to make my decision based on their comms style. But a developer who actually has to work with them? Yeah I could imagine it mattering.