It's a bit of both i'd say.
It's in the breeds nature to begin with which is why it's such a common occurrence compared to other breeds. They literally trace their lineage back to purpose bred fighting dogs.
Labradors are often in the top few breeds of dogs that are involved in dog attack statistics.
I think Greyhound owners are far more honest about what their dogs are capable of than Staffie owners seem to be. They know and can admit their dog can **** things up rather quickly. Which is why a...
Fans of Staffies often say they aren't aggressive.
And when they are taking about how they are with people they are probably correct.
Staffies however are always found in the top 2-3 breeds of dogs attacks on other dogs/animals going by statistics put out by councils.