They say that Eton English markedly differs from Standard English

Indeed, many terms that are used here are incomprehensible outside the school. For example the word "lesson" or "class" used at Eton. "Division" is instead. In the 15th century classroom was separated wooden division, hence the which is confusing to the uninitiated. There are hundreds: thousands of such examples. There are many archaisms "Eton English." Newly employed teachers are issued a special Eton dictionary. This language tradition has remained unchanged for the past 500 years.