An erection isn't necessarily porn. It is pretty necessarily sexual, I'm not really seeing any way around that.
Still, it could be commentary. It could be erotica. Fine art's gonna be tough, but not impossible.
If you're interested, I'd dig pretty deeply into the guy's motives, and I'd make sure there's a chaperone. Honestly, when people of opposite sex who don't know one another are working together for the first time, there should always be a chaperone if possible. It just takes bunch of possibility for bad things, but much more likely, misunderstandings and social difficulties, off the table.
Don't buy the "shoot one erect cock and you've ruined your career" theory one bit, though. This isn't 1898 any more. Maybe if you live in a very small conservative town, or work for a church, or something. But outside obvious special cases, nobody gives much of a damn if you shot a bunch of orgies last year. It's a porny world.