I think class may enter into it at this point. It's made clear elsewhere in the diary (in a bit I didn't quote) that some of the boys used to make fun of the Nurses for their social pretensions and use of "spicy" (i.e. hifalutin) words. E.g. there was a story of a Nurse reporting to the Steward: "Oh, Sir, when I was on my perambulations, I saw two combatants combating, and if I hadn't contifered, I don't know what would have been the insequences!"

So, it's not just a member of staff's word against that of two pupils, but a working woman's word against that of two relatively posh teenage yobs.