The NBA has said that the report is wrong and that there is no racial bias in their refereeing (duh).
The report only used boxscores and not data on which of the three rostered referees made each call.
The NBA says that its most recent report used data that included the caller of the foul and that their information showed no racial bias. Buuuut...
The Times said the NBA denied a request by Wolfers and Price to obtain that information, citing its confidentiality agreement with the officials.
...they don't want to give up that data.
I tried an online study a few months ago which used word and concept association alongside characterised faces of black and white faces. It mixed up all of these combinations and even showed black faces with typical white features and vice versa. I consider myself more tolerant and less biased than the average person, but my results showed that I had a slight inclination towards associating positive concepts with white features, and negative concepts with black features.
I'd say that there's a strong chance that no matter their good intentions and character, that there could well be a very slight racial bias shown by referees.