False Accusation, Persona Non Grata

(TL;DR: I don't know how to react to potential false accusations)

Throwaway for obvious reasons.

Today I received a letter at my college (USA) from a nearby university stating that I am no longer welcome on that campus and am considered a Persona Non Grata. This is following a complaint received a few weeks ago "that violated [name of school] policy."

The date of the complaint comes one day after the only time I've ever visited this school, for the purpose of meeting a girl I met on a dating app. Without getting too personal, we engaged in mild sexual behavior that was fully consensual and stopped when she voiced that she was unready to go farther. Stopped as in full stop, no ambiguity, no disrespect to her consent. A few minutes later, her roommate came in but seemed to pay me no mind. For the next 45 minutes or so, I tried having a conversation with the girl, who I had already decided was not my type and that I didn't particularly want to be there. I grabbed my things and asked her to walk me back to where I parked. I blocked her on the dating app and Snapchat on the walk back, then informed her that I didn't want to see her again.

The letter concluded with an invitation to call the given number if I had any questions. Naturally, I called immediately. I spoke with the school's Department of Public Safety, and a secretary informed me that the man I was trying to reach had left for the day. She texted him asking what he knew about the letter, and he told her to say that "the letter is pending investigation."

My question is: what might "pending investigation" mean? I'm freaking out and can't get answers until Monday when the office is open again. A friend pointed me to this subreddit. Also, if you believe "pending investigation" means there may be legal action involved, how best should I prepare myself? The accusations are unequivocally false, but having blocked her accounts, I have no evidence of the multiple invitations to come over and licentious messages I received. I expect her roommate corroborated whatever she said happened, and/or is willing to if need be. I have no witnesses, other than the friends I told about the night's events shortly thereafter. Thank you!

Edit: I am a male of legal adult age and she was a female of legal adult age. Sorry, not too familiar with Reddit. I read some other posts and figured it was assumed but not expressly stated.