It certainly makes sense to assume (in your head) the black guy is a rapper, and the white guy is a tech CEO.

But when you know how it makes people feel when you make your assumption visible, you understand the need to act like anyone could be the CEO, the developer, etc. Same goes for women devs who at tech conferences who are too often "assumed" to be girlfriends, recruiters or other non-tech participants.

Yes, the problem will solve itself if black people in tech become more common - but:

1. it's not going to get solved if we make them feel out of place in tech by always assuming they're "the wrong guy".

2. let's try not to make the life harder to the very few black people (and other minorities) who are already in tech?