I am not sure if I agree with that but not knowing the history means alot. There are time when you just do not have a good animal. I have been fortunate.
I have two little midget house dogs. Got the first when my daughter was little. I always blew into her face (just knowing what a kid would do) it has no effect on her, but she kisses back. Stuff like that makes a HUGE differnce when it comes to pets and little kids.
Line breeding? That may be why.
Though some are just, well, the way they are.