That is crazy. It is a guideline, not a law. Anyway ,the recommendation is '10-12 students per aduit. None of Easyjet's business IMO. And officiously OTT.
Unless the youngsters were being rowdy and uncontrollable, and there is no comment suggesting that at all.
Congratulations Easyjet official, whoever you are, you just ruined some youngsters' happy expectations, for no justifiable reason whatever. There really are some folk for whom any authority is a dangerous thing.