I love a good conspiracy or “syndrome”. But is this researched based? Sounds a bit like there could be other variables involved like breed.

Not sure if this is about racism. A lot indeed is, but this, not so sure. People love Jack Russell Terriers and many are black. How about Cairn Terriers, like Toto from the Wizard of Oz?

Would need more data to think this is real beyond urban myth and confirmation bias.