I don't know, maybe he's gotten so many rejections he's wondering what on earth is wrong with him, so he askes for some feedback. I don't know date sites, but wouldn't that be a nice thing to do ('I had a look at your profile but i think we're a little too different'), or is it not done?
I know 'no' is a full sentence, but wouldn't it be just a little friendlier? It seems like such a cold brush off, otherwise. (I haven't dated in a long time though, so don't really know the ropes...)