Most Black people in the UK live in urban areas. There are strong, long term, Black communities in nearly every major city, mostly hailing from Africa and the Caribbean, but growing Black communities from South America and Portugal, too. This long term presence has had an effect on shaping the culture of the cities to varying degrees. Music, food and fashion are three of the most observable ways they influence the areas in which they reside.
Going back to the two men:
If those two men both wear a Montclair (is that the right spelling?) jacket, they'd both be considered "urban road men" even though one has read Latin at Durham
To show that he isnt a road man, the graduate would have to avoid wearing clothes associated with "road men", simply because he is black. And even then, his clothes would be seen as a costume. And you know what? In some senses they may well be because he may prefer to wear a tracksuit and Montclair (still not sure!) jacket.
It isn't like a white man can wear the jacket and tracksuit without attracting similar criticism. He will and largely because that dress code is associated with being urban (read black) and so he is assumed to be of low class and character to desire to be associated with the such.
And it isn't strictly about professionalism, either. As pointed out in a recent thread on uniforms, professionals have more freedom than ever on what they wear to work. People nowadays romanticise poverty and essentially fashion is about looking shabby and low effort. Jeans, t shirts, beat up trainers, whatever. So it isn't a class thing where looking poor is the issue. There is a racial element where appearing to be black or positively influenced by Black culture is seen as the bad thing.