You should care if you agree there is discrimination in tech. If you are part of a minority and have never faced discrimination in tech, that might give credibility against such a claim.
Yes it is - it's a measure of interest in computers and drive/intelligence.
If you don't like AP CS test - pick some other parameter that indicates that this population that should (absent discrimination on part of money-bag holders) produce a number of startup founders.
Most schools don't even offer AP CS. Especially not public schools that primarily serve low-income students (which black people are disproportionately more likely to be). The course/exam is not equally accessible to people across racial demographics, and is, therefore, not a logical metric to measure potential (unless you're maybe looking at percentage of people getting 5s out of the total number of people of that demographic taking it).
How many black women got 5 on AP CS test?