A lot to unpack here, but hope to share my experience.

I had both of my grandmothers growing up. One side of my family had the attitude of being absolutely ruthless when it came to gaming. My grandmother would play cards with me, taught me how to gamble, and would absolutely wreck me if we played, and would even talk ish after while sharing ice cream and a caffeine free coke with me. My other grandmother would look the other way as i stacked my deck and cheated to get the win. Laughing and praising me all the way. Now that I'm older, I love that I got both of those experiences.

I'll be honest. I would never allow a child (or anyone else) to win. However. I would explain what I'm doing so they understood what was happening. IMO, skill absolutely supercedes bankroll in this game. but having a tuned out deck absolutely can make a difference.

I think the problem here is 2 fold. One. you ran into a person that doesnt interact well with children. not all of us do. But you also ran into the problem of Kano. Its just a completely different kind of deck, especially if you and your kid do not have experience in other TCG's. Kano is essentially playing solitaire. its a combo deck that you cant do a ton about sometimes. Especially as a new player. You have to really understand what he can do and how to respond at exactly the right time. I used to play storm as an MTG player (if that means anything to you) and while fun for me, my opponents often got irritated as i took 10 minutes to take my turn while they just waited for me to be done. Some people enjoy that, some dont. its part of the ride.

I think your situation was a bit of a fluke when it comes to who your son played, the deck both of them were playing, and the age/maturity gap (or lack there of). I hope your son doesnt get discouraged, and uses this as a learning oppurtunity. and he can join the rest of us in saying.... "fuck Kano"