Here is my honest read on the situation,
I read this as black belt who thought he was in for a casual roll repeatedly tapping a blue belt trying his go-to game with illegal techniques after it was more of a challenge than anticipated. After you get knocked off your base you think, "oh your going to go for a berimbolo!? Fine, ill see how you like a knee bar then." You slightly disagree with his game, because like many black belts, probably only first learned the berimbolo at purple/higher belt and think that others need to learn it in the same order.
The tough young blue belt represents something greater than what happened in a single isolated roll. It bothers you more than any other unexpectedly tough roll because of what he represents. He represents a mentality that is out there and but only partially understand. On many levels, you watch other competent grapplers try and kneebar and toe hold great berimbolo guys and know that those techniques would have likely not worked in a few more years when he learns to protect his feet better.
When we have to actually "try" when we expected to do close to whatever we wanted, this highlights the presence our ego is undermining long term progress.
For starters, I think its common for upper belts not to respect lower belts skill and threat they could pose on the mats. Look at many old school guys attitudes towards lower belts. I KNOW there are blue belts and purple belts that could beat me in a competition setting. Most don't - but I know they are out there and occasionally I run into them. I respect each one I roll with and if there is any guidance that my experience can offer them, I will while all the while recognizing in a few years they could surpass my Jiu-Jitsu knowledge and ability. This was a lesson I learned early watching a dorky looking 15 year old kid with braces giving some of my toughest training partners a hard time. Now everybody knows him - but nobody did at the time.
My suggestion is, instead of being competitive and slightly adversarial with this blue belt, is to learn from him instead of looking for sympathy against a 1 dimensional blue belt being for being one dimensional. He has something to teach you and I. Try going into his DLR guard and see if you can prevent him from knocking you off your base without resulting to leg attacks. Try letting him recover if you step over a leg and get in tight. This guy might have only 3-4 years experience, but he probably has 2 years of obsessive compulsive berimbolo knowledge behind him. Somebody who thinks like this kid - but with more experience - could be sitting across from you at your next tournament.
More importantly, share with him what you have to offer about a more old school mentality. If he melds the two together, perhaps instead of the dorky young kid with braces, he will turn into a Liera Jr. with the benefit of your experience.
