People have sex with sluts all the time.
I don't know exactly but there is something psychological that takes place if a person pays for sex as their first time. I don't know the affects and so on, but a "variation" did occur with you. But you didn't know it was taking place/you didn't pay for it.
Regardless who cares. Tell your friends thanks both of them were great.

You say both*** because that would mean there was another girl involved that they didnt pay for. Lol nvm, who cares what they say.
And yea I don't know if they did you a favor but if my first was paid for as a joke like that I'd likely break their nose & call it even.