Black people make up 3% of the UK population according to a quick Google search. If there are 7 black people in his company of ~250, that's almost 3%. This is just one data point but it's the one he's using in his post and getting upset over the lack of black representation, when it's proportionate with the overall ratio of ethnicities in the wider population.
44% of London is black.
We are still waiting for the results of the current census. Where did you get the 44% figure from?