Is it just me or does his message sound red-flaggy?

In reference to me complimenting his look for today and flirting: "relax your mirror selfie was way sexier, you better watch out I might get you pregnant on the first date 😂 . My sperm are strong haha"

I've made it clear that I'm looking for something serious and not a hookup or anything casual (and he had said that he's looking for something serious too). Reading that message made me uncomfortable and sounded rapey to me. Before I let him know that it made me uncomfortable, I want to ask here if it sounds bad to you as well.

UPDATE: I let him know it made me uncomfortable. He apologized and said that he won't joke about it again. He also asked me what kind of sexy talk I'm comfortable with and what I'm not. Green flag?