Of course some notes are off, it is pretty challenging to take one guitar, bass and drums and trun it into a musical piece that a full band can play.
You could tell what the song was and you did agree it was fun to listen to, but ya really can't dissect it. It's all in fun and that they did!! Would have loved my band teacher to let us play modern stuff like this.
Also pretty awsome your director would pack up and let ya'll finish.