Was your school 90% Catholic?
Forget the SP episode, any image of prophets of Islam are strictly prohibited afaik. The reach of this should not extend to those who are non believers.
Curiously though, it's my understanding, the reasoning behind this is to stymie our tendency to worship the tangible. Christian's share the same sentiment, but the progression of each religion differed and here we are.
All that being said, I still don't see the OP as some huge problem. It makes sense from the schools district standpoint. Google yields articles going back 18 years regarding Dearborn introducing halal certified foods. Seems it progressed to the point where there was enough confusion about which specific school ordered what, and where it was actually ending up and the district just said eff it, almost all our school lunches require halal meat, let's do this.
And frankly (no pun intended), the meat in the certified PDF doesn't even appear to be better, just had the right words said to it. I couldn't eat those hot dogs anyways (maybe during zombie apocalypse lol)