Yes, it will feel like your whole belly is tightening with BH. Also, a BH will typically last longer than like a big movement or the baby pushing out or something, which also tends to be more localized. It is kind of a similar feeling though, IME. I can tell the difference, but only because I've had both. I can see how you might wonder which is which.
FWIW, I didn't notice any BH with my last pregnancy, but have with this pregnancy.