"School bullies pick on any difference, it could be height, fatness, wearing spectacles, going to the 'wrong' school, having ginger hair or freckles or any number of things. ypu don't have to be just black or gay to get bullied, believe me I've been there."
So have I.
I also know what it's like to grow up as a gay teenager in a UK school. I can remember how all my classmates would use the word 'gay' pejoratively towards just about everything, and I remember there was often pressure among the boys in my class to appear homophobic ("I hate gays" etc.), when in retrospect I don't actually think they were.
I also know that in retrospect that when they said a lesson/accessory was "gay" they didn't mean homosexual - but that's not something which was abundantly clear to me at the time. I've also gone into schools and done workshops on this kind of thing. We often had young gay teenagers approach us after the class has left and confess to feeling isolated and unhappy.
The feeling reported by stonewall, in my opinion, is genuine.