QUESTION - Are gym erections normal for guys?

Hey there! Just came back from the gym with the guy I like. We were doing leg day today and he had an apparent boner by the end of our workout. Is that normal?? Do guys get hard during workouts of was it because of me (I did see him checking me out during squats)?

Some background information -

We have been dancing the line between friends and more than friends. Two nights ago, we went to sleep in his bed together after a party and cuddled (he got hard then as well). I haven’t made a move because our friend group dynamic is complicated at the moment and I am unsure of whether he truly likes me. I posted a bikini picture from my day trip today and immediately after I got back, he invited me to the gym with him.