Do you think they are your friend? How do you define what a friend is?
When you appear to be a nice person, people who don't know you will treat you nicely - that's just being human. There's a huge area between friend or foe of people who just accept you on face value and mean you no harm. It doesn't necessarily mean they're your best buddy and want to go down the pub with you.
I have lots of acquaintances that I would meet socially - but very few close friends. I suspect most of my close friends are diagnosed or undiagnosed Aspies. Most of my casual acquaintances are NTs.
Yes, I would absolutely say that to someone I cared about.
It's a positive, supportive statement.
It sounds like they want you to know that they are there for you. Whether they are a friend/acquaintance etc is hard to say - only you can know that. But it's a very nice thing to say to someone, and shows they care!x
Much love <3