I wonder if they're just used to being around non spayed dogs / so they're kinda on edge in a way.
Local suburban / trained dogs around here mostly just want to play with each other / random people / kids. I think they might be used to that kinda lifestyle even if just by example from other dogs.
Lots of people back home would keep their dogs in the yard all the time. The dogs wouldn't really ever socialize with the neighbours' dogs (maybe that's the issue?) For a lot of these dogs, if they ever got loose, they'd go and bite someone as soon as possible. This is true even/especially for the dogs of the rich, who have very easy lives.
But with Canadians, I'm never scared of their dogs, because at worst they'll hump me!
Depending on where you're from, some places spay / neutering dogs is much less common. It can impact their behavior a great deal.