Given parks allow children to enter parks at 14 without parents, and many parents already have children much younger riding school buses, I wouldn’t think it's rare.
No, it happens but it is a sad world we live in if it was common. Buses are public, it would be even more rare for a child to be the only one on a bus in a place like WDW. At 14 years old their parent should have taught them what to do in the case of someone attempting anything. Even if a person were inclined to a certain fantasy, acting upon it while others can witness would even be more rare. The foolish idea that someone is "grooming" anyone while driving a publicly used bus has an imagination more corrupt than the people we are talking about.
How do you do that while driving short distances within a short time that anyone is riding a bus in a resort? The law enforcement guy that made with the award winning theatric in that video tried to imply that the guy was pulling the bus over and either "grooming" or Texting while on the clock. Take it from someone that has driven buses. The only time you would have for that is on a lunch break, not while actually driving people around. This guy was a sick individual. People like him are not the majority. There is a bigger problem for that from the "guests" that are sometime packed in like a can of large sardines. Besides all buses these days are tracked constantly on GPS. If they were stopped in a place they shouldn't be, it would be known in real time.
I once complained to Disney when they had, maybe they still do, a policy of shutting of the interior lights in the buses at night between stops. Talk about opportunity for some sicko to have a good time. That we don't think about but a guy that is driving a 10 ton vehicle though traffic while being expected, by the passengers, to entertain them, isn't going to have time to do anything else.
This guy was sick and I'm sure we all come in contact with people everyday that are not well, that doesn't mean they are an immediate danger nor that anyone would ever know what was possible no matter how many background checks were done. We don't expect that from a CM, but that is part of our fantasy that Pixie Dust will prevent it. I lived for years in a city that only had half the population as the employee count at WDW. And that isn't even taking into account the 10's of thousands of guests on any given day. There are only two things we can do. One is to stay in our homes and hide in a locked shelter or inform and train our children of any age about what to do to prevent that from happening and mostly pay attention to what is going on around you. That would prevent many of the problems.