So my thoughts...
Some people seem to be rushing to defend the OP's honor, however the incident is over with and what she got out of the experience ended up being positive for her and she's taking the time to reflect upon this experience since she's struggling with the acceptability of allowing a perceived violation upon her person.
So first, what does it mean to be molested? To molest is to bother, annoy, interfere with, make indecent sexual advances towards.
By definition, the person who had initially started touching her, was in fact molesting her since the intent was to make an indecent and an unsolicited sexual advance towards her.
Now the question is, was she violated? So to violate you break, infringe, or transgress. To break in upon or disturb rudely, pass force without right, treat disrespectfully, molest sexually.
Now initially I think we would all agree that she was violated. Hand on the ass from a stranger would not be typical or acceptable behavior. However at a point, the OP decided that she liked the excitement and the thought that she was in fact being violated, and from that point it was consensual. She could have done many things, such as scream, move away, punch the violator, etc. Instead, she allowed the man to feel her and then exited without further incident.
If she had arranged this meeting prior, then there really would be no issue. Now the thought is if it's right or wrong, demented, delusional, totally hot?
I think if it floats your boat, then you shouldn't feel as if you did something wrong or that you're in any way deviant, since in the end, it's what you want and what you allow. If circumstances were different and you were forced to be molested against your will, and after reflection, you decided that you in fact, had enjoyed it a lot. Then I would suggest counseling
As for her allowing the stranger to feel her in the subway, yes, it may encourage him to try again with another stranger he encounters. The point is that nothing is known for certain. Maybe it was an accident and he noticed that the hand wasn't moving away and he was feeling around and it was really hot for him as well. Maybe it's an old pervert who lurks in the subways to find young prey. Either way, it's unknown and if you're put in such a startling position, you may not know what to do. It's not upon her shoulders to weigh all of her actions in a manner where she decides upon the consequences for the greater good.