Staying hard after cumming?

So this guy I’ve been talking to/dating is super experienced with sex like way more than I ever will be. When we have sex and he cums I noticed that he stays hard afterwards. Maybe not completely rock hard but still hard/usable lol. I’m just super shocked by it because usually after a guy cums it goes completely soft. Is there a reason why it stays like that or how he keeps it hard? I’m so curious lol.