You are not necessarily wrong, but you kinda being a little selfish. There will always be somebody who plays better than you, ALWAYS. So, if your only concern is about him playing better than you, then u need to get out of that mindset real quick. That just leads to jealousy and envy and all those unholy things that will get you in trouble with God.
But, reading you post, I don't think that is your only concern, the other problem is you the one spent the money on them DVD's and now he just trying to get it from you so he don't have to buy it. I feel you on that one right there. It's just like with CDs, you go spend your hard earned money, then somebody want a free copy. You just want to tell them, "Go get your own and stop bothering me." But then again God does love a cheeful giver. If you bless others, God will bless you.
Sometimes, every now and then I be debating whether or not to put some of my chords on here cuz then people will just steal them and then there will be a whole lotta copycats. I be like I spend hours and hours trying to learn this stuff, and then peole just get it and run with it w/out putting in the work trying to be original. But, when that thought comes to me, I shake it off remind myself who I'm doing this for, God. If you can use my chords to help your playing, then that's great. I want God to get the glory instead of me. So, I will say this to you RJ, if he wants to borrow some of you DVDs, go ahead a let him. He may not even understand the techniques like you do and he will probably still come to you for help. It may not be fair in your eyes, but it's right. You should be concerned more with doing what's right than what seems fair.