I read there are ~ 100 HBCU's, not sure of mix of public vs. private. Specific to D1 athletics, I'd guess there are less than 25. I know the MEAC & SWAC have a lot.
With this signing, and them being private, well known and in major city, I can see how Howard U and a few others can make inroads in NCAA basketball in short order. A few big time pro donations can help expedite.
That said, while SJU is not a HCBU, it can be an increasingly attractive option with Anderson and staff at helm, major city and high diversity among students.
Key is for any student athlete to pick the best fit - whether that be location, coach, diversity, playing time, academic options etc.