At least it was an easy A.
Yes, PHP is a language, and Ruby is a language. PHP does a lot more than that. A default install of PHP + Apache has routing logic, and HTTP parsing (what populates all those superglobals like $_POST?), it has templating (I'm sure ERB came up with all of its syntax independently), etc etc. In the Ruby ecosystem, you those are responsibilities of a "framework". Indeed, no one would argue that Sinatra is not a framework, but I'm not aware of any features of Sinatra that aren't already delivered by PHP out of the box.
If your goal is to build an artificial and incoherent taxonomy of "languages" vs "frameworks", then yes it's very clear that PHP and Rails are different types of things.
If your goal is to actually build web sites, comparing Ruby+Rails (which you might write as "Rails", since it implies the "+Ruby part) to PHP is a very reasonable thing to do. I think it's utterly clear that the GP was comparing "making a web app with PHP" to "making a web app with Ruby and RoR".
Here's why I think learning Rails would be good for undergrads: You get exposed to patterns like MVC and stuff like server vs client, requests, basic auth/security in a format that is practical and presents itself to fast iteration and quick feedback. I'd much rather learn MVC through Rails than the extremely dull and slow Java GUI apps we did in school.
I think the magicness of Rails is overrated for a beginner. A lot of people like to tinker with low level stuff, but in my experience in college most students wanted to build stuff. Having them build their own routing/template/controllers/etc or whatever would've been less interesting than just learning the high level concepts with Rails first.
As an added benefit, having some experience with Rails would've helped some students get internships.