So... wait... are you saying all these white people in BLM marches...
You're on a very slippery slope, my friend.
The poster is talking about things more akin to, say, a non-trans person speaking about the experience of being trans or someone who has never went to college speaking for college graduates - when really, they shouldn't try to speak for groups they aren't a party to.
In other words, I can talk about prejudice and racism I've experienced and witnessed, but this doesn't mean that I have the credentials to talk about what it is like to, say, have dark skin in the US and experience that sort of racism. It just isn't the same, and I don't have that experience. After all, I can (in the US) basically just be a face in the crown in a small town.
Or is this "community" thing a political thing, where members share a narrative? If so, why do they get to claim the badge of "Black community" from other dark-shaded folk who aren't like-minded?