I can't believe it, I read through this whole thread and nobody was intelligent enough to come up with any answers, actually Sean Michael came the closest. There are a couple possible explanations one more likely than the other.
1. As Sean Michael said, he is hitting his prostate, It is the only way a man can ejaculate without some sort of stimulation on the perineum and frenulum, this is located just below the bladder, so a correctly angled punch could possibly, be hitting that area.
2. He has a female "g-spot". While unlikely, sometimes God screws up and gives female parts. Stimulating the female g-spot (about 3 inches above the vaginal wall, below the belly button, can make a woman secrete a clear ejaculate (aka squirting), this doesn't happen with all woman, and is even less likely in men but still possible, so if your man goo is slightly clearer well (and sugary as opposed to salty, you will have to try it ha!), you might just have a cool gift.