These incidents happen on a regular basis on public transit in California, and on that trip similar things happened to me a few other times. It's not comparable to European transit systems at all.
Only because in Europe so many more people ride transit. The number of people who will be like that is generally fixed per population, and so if you have a lot of other (normal) people riding they a smaller %.
As a daily commuter on la metro bus and rail these incidents aren’t as common as people make out online. Nor do they ever really affect you when they happen.