What do you think? Options

[Harp]

My friend has kinda a big problem.
Which he says is fixed, but I don't think so.
AND IT IS MY FRIEND. THIS IS NOT ABOUT ME.

I guess that, he's been friends with this girl for a while, and she started to like him.
Well, he had sex with her without them being already IN a relationship, and afterwards, there was no relationship established.
She's been calling his phone for the past few days, not leaving him alone for anything, and filling his phone with text messages.
He says it was only a one night stand, and that he thought she was aware of that.
Turns out, she thought they were in a relationship, which is why he wouldn't leave him alone.
He kinda likes this girl, but didn't want a relationship with anyone.
Now that's he told her it's only for that one night, and there was no relationship at all, she's decided to go off and spread rumors of him being a player and such.

Do you think he was wrong for not telling her directly?
Or was she wrong for blowing it out or proportion?