Probably not. It sounds like the Apple TV might be on a different VLAN to the guess network (basically a different network if you want to put it really simply).
You could try setting up a Plex server on your mac.. Seeing if it will let you share the content externally (to the outside world) and then use the Plex app on the Apple Tv to download the content. Probably a long shot on a restricted network but worth looking into....
With some managed wireless systems (like the ones used for massive site deployments) you can isolate each wireless client to stop peer to peer activity , so effectively you cannot see each other even though they are connected to the same network. I'm going to guess that is what is stopping you here and when you are AirPlaying its using bluetooth instead of the WiFi because thats the only way it can see your Apple TV.
Short of creating your own network and putting a router between yours and the college campus guest network i would say just get a HDMI dongle for your Macbook and plug it into your TV when you want to watch files stored on your Mac.