To play devil's advocate, he may have had suicide prevention training where staff are encouraged to check in on people by starting a simple conversation.
I don't work in this industry but do have suicide prevention training where we are encouraged to engage with people who come across as a bit down.
You've basically said you were at the far end of a platform and were trying to avoid people.
Unfortunately train stations and train tracks are hot spots for people taking their own life.
I have reported to train staff when I spotted someone distressed on a platform bench and a teenage girl crying in a platform toilet cubicle.
If you feel unsafe about your interaction do report it.
I just wonder whether your demeanor attracted attention so this staff member was undertaking a discrete welfare check.