I will repeat what was written here. TWO chop block calls on the defense. No explanation given to the player when asked.
We really need good officials. Guys that know the rules and how to enforce them. And when asked, how to explain what the foul was so the player(s) don't repeat the foul.
I have seen hundreds officials in many different sports who are really, really good. They know they aren't the reason people have plunked down their money to come out and watch a game.
And have seen a few who need some work studying film, reading the rules and learning a bit about what an authority figure should be.They want to be the center of attention.
To me, this is one of those guys.
The defense cannot block below the waist outside the free blocking zone, this is a "safety foul" that probably isn't called enough. That may be why you have not seen it called, but certainly doesn't make it wrong to be called.
As for the explanation not being given, often times kids will ask the closest ref what the call is, and many times it is hard to explain what someone else saw. Also not best practice to explain something you don't know to be 100% correct