Well, since you own it, and aren't willing to share it with him, he posted a plugin request for the exact same thing. Can you blame him? No. He's copying the plugin exactly, but only because you won't give him a copy. I'm not trying to say you should give him a copy, I'm just saying that it would be better for everyone if lots of these private plugins were released for the general public. You're going to have multiple people code the same exact idea multiple times.