Depends what you tapped him with, and also depends what he was doing.
I have tapped my main MMA/grappling coach with a toehold 3 times. I have only taken about 2 gi classes for BJJ. He has held a purple belt for several years and is pretty close to getting into the UFC. But I don't get proud about this, because it's just rolling in the gym, plus it's a leglock. I can only catch him with that move because if I even TRY to engage in the BJJ game with him (positioning and guard passes), he wipes the mat with me. So my point here is if you're catching a BJJ guy with a move predominantly used in other forms of grappling (not saying he's a "BJJ guy" or that BJJ doesn't have toeholds), you have the suprise factor working for you.
On the flip side, I have been tapped by people, both heavier and lighter than me, who I have much better technique than. The main reason is because in the gym, I always go for moves, and never stay still. It's not a competition, so why should I be conservative? I go for crazy shit, and try to work out of any position I'm in. This is especially when I'm much more technical than my partner. So every once in a while, I get a little bit too lax, and I get a wake up call with a basic kimura or something.
Sure, give yourself a little pat on the back, but the absolute last thing you should ever do in the gym is think "I'm better" or "I'm the best." I DO think you should be thinking "Hey, I'm really good at this," because a confident attitude leads to more productive workouts. But never accept your performance in the gym as an accomplishment. This is for 3 reasons:
1) You'll hold on to "victories" in the gym, possibly preventing you from entering actual competitions or rolling with harder partners because you don't want to ruin the ego you built on the mat. (If you haven't competed, IMO, you haven't really achieved anything, and if you're not getting your ass kicked, you're not getting better)
2) You'll ease up too much on your training, because you assume you're already good.
3) You'll be too emotionally attached to whether or not you "win" in training, preventing you from ever really taking a risk to learn more.
Be proud, but be realistic. You had 50 pounds on the kid, and most likely, he wasn't playing all that conservative. Nice job, and keep up the good work, but find someone who's at your weight, or heavier, who can beat you the majority of the time.