I feel like that's the whole point of the OP. I agree with the overall post but mentioning the ICE relationship seems to detract from the main point.
"I hate GitHub because X Y and Z features are bad" is a good reason to move away; "I hate GitHub because one of their thousands of enterprise customers does not align with my political views" is not, in my opinion.
For the record, I do not support ICE
I read it as "this was a big news story which we care about. You may know it, but it is not the primary reason. Here is the primary reason."
It does signal/imply that even if GitHub fixed every technical grievance tomorrow, Zig might still not come back.
People protesting ICE do not do so out of political concern, but humanitarian concern.
This seems like a minor nitpick as those two are intimately tangled up, but it matters to make the distinction. Standing up for others is not petty or self-serving and that's exactly what this sort of conflation can falsely imply.