No, I don't think it's a bad thing, but if he wants something casual he's handled it really badly. Rather than go on three dates where this wasn't mentioned, and then just sleeping with someone else and telling her about it out of the blue, he could have been upfront from the beginning about what he wanted, so nobody is wasting anyone else's time.
He didn’t say that he wanted something casual with the OP, they simply are casual at this point in time. That doesn’t mean that either of them necessarily want to keep it that way, but they haven’t progressed beyond that stage yet.
I just find it incredibly odd that he has told her after the fact that he's slept with someone, but in the same breathe he still wants to see her tonight.
I would find it incredibly odd if he gave her a blow by blow description of it, if you’ll pardon the wording, but it’s pertinent information for her to have, clearly, since it prompted the creation of this thread.
Unless you mean you find it odd that he’s slept with someone else and is still interested in seeing the OP, in which case, why is it odd? They’re still at the start, where everything is new and interesting, and they’re sussing out where things are going. Seems normal to me.
Oh yes, silly me, men never 'game' women, there aren't whole swathes of the internet dedicated to negging and abusively manipulating women, with men videoing themselves taking part in these tactics and posting them online, I must have imagined all that...
Except there’s been no negging or emotionally abusing of the OP described here. He slept with someone while he and the OP were still at an early casual stage, and he informed her of the fact. I’m not sure how informing her is in any way a bad thing, unless you’re of the sort who finds ignorance (of the facts in this instance) to be bliss?
In which case, you’re welcome to it, but between a choice of being forthcoming or concealing something that may matter to the person, give me forthcoming every time.