Honestly, it sounds like even acknowledgement was not the problem. Their coworkers did speak up -- to criticize the protesters and claim they weren't accomplishing anything.

If I were in this person's position, silence would make me feel a little weird. My coworkers actively deriding the protest that I'm about to go join would make me feel a lot more weird.

I don't think people are lying when they say that tech employees have their own biases and blind spots, and it doesn't necessarily surprise me to learn that race is one of them.