I was called a nice guy by a woman and I don't understand why.

I was talking to a woman in my office and the following discourse took place:

Me: Once a girl lightly crashed on my motorcycle with her scooter. Traffic was heavy, so instead of stopping everything I told her to watch where and how she drives in a stern voice and went my way. My motorcycle had a mild scratch which was not something that bothered me that much.

Office Woman: Oh u r such a nice guy.

The question that pops in my head is... Why? How?

So now I am supposed to flip my shit every time some one touches me or my possessions inadvertently? Do I have to be so brash as to totally give up civility? I realize I might be taking this too literally. I should come off as someone who just shouldn't take even a little rashness from others and probably show them their place, but shouldn't my response be according to the situation? In this case, it really didn't bother me because the traffic was bumper to bumper and getting rear ended was a huge possibility, and I didn't even get a dent, just a slight scratch... on my exhaust. I don't understand how am I a nice guy in this situation, please help.