He's black and they're cops. Black = criminal to most NYPD
Duh! And clearly NYPD aren't the only police personnel demonstrating erroneous belief in your equation. Maybe if James had pleaded for them to ask Johnny Mac or indeed Andre Agassi to ID him, they might have only held him handcuffed against the building for 20 minutes.
BTW, James Blake, although clearly of black ancestry also has a white mother (similar to President Obama).

James to me seems very easygoing and a blissful soul. Despite being unfairly targeted and roughed up, James was probably very polite to the officers in question and he likely has no interest in further discussing the incident.
ETA: And I wrote that last sentence before I read
@Vash01's post, which apparently confirms my observations about James' temperament. Although, I see that James was disturbed and upset about the unfair harassment, and he has not returned calls to NYC police commish.
Unfortunately though, not only are cops known to harass and/or to kill black males (whether or not they are law-abiding black males) at an unprecedented rate, clearly it has become such a commonplace occurrence as to be expected. Fortunately there are poets like Jericho Brown (see his books,
The New Testament, and
Peace) who question and damn such expectations. And yes, further comments on this topic are more appropriate to be posted in Politically Incorrect.