Having freshly graduated high school only this past June, I can assure you that this story, while maybe a hoax in this case, is not at all farfetched. I was frequently asked to stop using Firefox or Opera while simply doing research or otherwise school-related work on the library computers. I went to a public school in suburban Chicago.
Of course, I never really offered any resistance when asked to refrain from using superior browsers, because I didn't think it was worth the trouble. But I'm sure I could have ended up with a detention if I tried or handled the situation stupidly.
Microsoft rules with an iron fist at most public schools in this country.
Now in college, I am able to use any browser I choose on the school's computers.