Question about orgasming without cum

Last night I was riding my boyfriend and I knew he was about to cum and he told me he was about to cum...and all of a sudden he orgasmed...but a few seconds later he goes "whoa, I didn't cum." I was like "what?" and he said he felt it about to happen and at the last second all the pressure from the angle I was in kind of closed off the event of cumming, but he still felt an orgasm. Has this ever happened to anyone else??

And yes, I'm gay.