"I'm 100% str8 so why would my dick get hard with a guy giving me a massage? This can't be normal. I mean, I heard guys get hard during a massage so I asked for a dude so that wouldn't happen. there's no way he coldn't notice it but he didn't say anything. I mean, the head was poking out the top of the towel and the whole thing kept waving around while he was working on me. he never touched it though his hands brushed against my nuts a couple times. thank god he never said a word after when I was leaving. wtf was that about?"
I'm sure he noticed. He didn't say anything because his training prepared him for just such a situation. Because it does happen. It is normal. A physiological function. It's usually a result of complete relaxation. Your cock doesn't need stimulation to get hard, those spontaneous BOE (blood oxygen erections) pop up all the time. Add the movement of your body and, well...it'll just get harder. Lots of men try to stave it off during a massage by thinking about something completely non-sexual, but it doesn't always work. As you found out.