This is 100% on the winning coach. Blowouts happen and shouldn't be apologized for. This is a willful act of poor sportsmanship and complete lack of any sense from an awful leader of young people though.
The protocol is pretty clear for basketball. Once the deficit reaches 30-40, all players on the floor are subs. Tell them to run their regular systems (with the exception of full court pressing or half court trapping).
When the deficit reaches 80-100, you no longer need to run your offense. You just go four corners and pass the ball around to run out the clock. With the score deficit and talent disparity that great, nobody is getting any better playing actual basketball.
For the deficit to reach 150, like in this case, with anyone on the floor from the winning team still shooting, shows me there is a coach that has no business being a leader of young people.
Similar common sense rules apply for high school football. 40-50 point deficit means everyone on the field should be a sub.Tell them to run their regular systems (with the exception of downfield passing and really limiting blitzing).
As the deficit reaches 60-70, every play call becomes a fullback dive. If it passes 70 and is heading toward 80, you tell your QB to take a knee and run out the fourth quarter. Or at least run a FB dive to some of your worst athletes as fullbacks. It's really so simple.
There shouldn't have to be a rule enforcing a protocol like this. Common sense should dictate that that is how leaders of young people would handle it.