Humans can do similar actions for dissimilar reasons.

There are a myriad of context clues used in devining others' motivations. I'm sorry to say, here there is not, and is not likely to be, enough information to come to a reasonable conclusion in this instance.

Either motivation you ask about could apply, or none of them.

If you really want to get to the truth, I suggest having an open and frank conversation with the girl. Be willing to listen to what she has to say without contention. Take her words, think on them, and make your own conclusions as to their veracity.

As others have pointed out, consent should precede spanking. Your (re)actions are yours. Look into yourself to figure out why you are willing to act without consent, and if that is something you would like to change about yourself.