If you are referring to his video from May 2023, "Why I deleted GrapheneOS", it is about the team lead, Daniel Micay, not about GrapheneOS itself. He, in fact, praises GrapheneOS to no end in the very same video.
If you with "he" mean Daniel Micay, I unfortunately agree, based on observations from previously having idled in the GOS Discord for a couple of years. Plenty of downright mean and unforgiving behavior, not seldom due to him misinterpreting others' statements and questions.