Sexual acts, in and of themselves don't make folks straight, gay, bi, or anything else. I wouldn't worry much about the label. If both parties enjoyed themselves who cares? But if you absolutely insist, I'd say that the situation sounds "gay adjacent", at least. But that doesn't make anyone any more or less gay than before. In the end, it is context that matters here. If this was the 25th time he'd shot a load into another guy's mouth, I might start to wonder. But I generally take a person's word when they tell me their sexual preference. Sexual preference is something stuck in each of our heads. Each of us has to determine for ourselves what our sexual preferences are, and that is something that isn't up to others to do for us, nor should we do it for them (which we can't anyway).