As a 6' 2" black man, I can relate to how both parties would feel in this situation. I keep distance and sometimes even cross roads when passing women at night. I notice discomfort in body language
I've done that a few times - and I'm white, but 6' 3".
in the past it used to be taken for granted that people were described by their skin colour or sexuality
Ah yes, but only of they weren't white and heterosexual!
But that's flippant. The casual use of 'gay', or 'black' as a first point of call to identify who someone is can betray latent racism, but too many people (mostly white) are so terrified of being perceived as racist that they can't bring themselves to use skin colour as one of a variety of defining features to identify someone; 'that guy over there, the one in the corner' 'what, the guy with the long hair?' 'no, the other one, the one with his side to us, the one who's a bit taller' when 'no, the asian guy standing next to the black guy' is more appropriate, obvious and straightforward, and could just as easily have been 'no, the white guy next to the group of black guys'. All a bit clumsy, but you get what I mean?
I love to know about people, about their backgrounds. My family are pretty mixed, though European (Irish, English, German, Hungarian Jewish, a bit of Huguenot) so when I come across someone casually who looks or sounds like they are from interesting origins I'm quite happy to open up a conversation about that. But my son once called me out on it as being unacceptably intrusive. Maybe he's right, but after sometimes a bit of initial reticence - understandable if they've previously had that 'where are you from?' 'Bulgaria' 'why don't you go home' conversation, pretty much everyone is happy that you are interested in them.
What I want to say is that if what is perceived as 'acceptable' gets in the way of straightforward human communication, then in my book it is unacceptable.