This is a boomer level of paranoia, and the logic is akin to “I once lived next door to a serial killer, so now I assume that all of my neighbors are serial killers”.
There are many places where its best not to play with the odds. And that person you replied to literally had real life experience backing it up. Theres a type of American that cannot stand being told what to do or someone suggesting they are wrong.
There’s a type of person who thinks that their “lived experience” trumps facts or logic. That’s why you have people who justify their racism based on a few bad experiences they had with black people or something. I try not to get in arguments with those people, because it’s a waste of time.
Thats taking the wrong lesson from things. Its completely appropriate for someone who witnessed a stabbing on public transport, to decide that talking to strangers on public transport is more dangerous than they would like. Its not racist or any -ist, its the basis for risk analysis.
You should also consider that public transport and who uses it can change immensely from one place to another. In my area, public transport is inherently risky, not to mention inconvenient, and people avoid it if at all possible.