I usually don't enjoy when people make assumptions about me, or take advantage without asking my permission, but horny sexual activity usually wins the moment. In this day and age, only a fool would cross or ignore unspoken sexual boundaries, but horny fools can be a lot of fun. I have experience with two licensed massage guys who decided to "jump" on me without knowing anything in legit spa environments. One guy was crazy horny (I assumed), and I was not attracted to his face or cock. At one point, he insisted I suck his cock, and I refused. He gave a great, strong massage, with major, helpful stretches. I think I saw him one or two more times, but he couldn't control his aggressive, horny state, so I stopped going to him. The other guy waited to the very end. Without saying a word, he shifted gears and worked to get me aroused. Not only was he a great masseur, I was attracted to him. I later thanked him for the surprise. I was traveling, so I knew I would not see him again.
No matter what, I've never gotten on a massage table with clothing on. For me, that's a red flag for strange. I have asked to be draped, because I don't enjoy getting cold. I don't have modesty issues, and I'm mostly up for a sexual surprise. So contradictions exist.
Way too many talented fish in the sea to prevent moving on. But minds change. If you get erect just thinking about the experience, then I would probably return for more. Sometimes, certain details can grow on you, and then no attraction becomes some attraction. If there is no chance of replacing his talent, and sex is a no for you, then you need to be honest with him. But given that strong erection, and that super quick orgasm, it sounds to me like johnny had fun, and wouldn't mind more.