Of course the academy is racist. It is racist as a group, by the nature of the proportion of older Whites in the academy being not reflective of the population, and by the fact that we know that in a large group of people, there will very likely be some who are racist. That is bound to affect the selection of nominees and the votes of those nominees. That is not to say that all, or the majority, of individual academy members are in any way racist.
Do all the academy members see all the movies and the performances that they vote for? Of course not. They will vote for many reasons beyond the performance and they are influenced by many factors, whether it is down to how good the marketing is that is aimed at academy members, or if they know somebody involved in the movie, or if they have a positive impression based on reviews. There could be a hundred reasons, but in addition, I would hazard at a guess that older White academy members are more interested in and more informed about "White" movies than "Black."