The professor may be teaching a Creo 3 course and may have to wait for the school to be authorized/licensed to move to Creo 4 under the PTC Academic program and to update any school computers.
It's pretty common for people to think that all programs work just like Microsoft Office and allow the ability to save in older formats**, because that's the office group they used before. It is a shock that this is rarely true and I don't know who should be one to carry that information. Microsoft is forced into this position as it would have trouble selling that all users have to upgrade simultaneously. I don't know the details of the Academic program, but I expect a student is only allowed the latest Academic version; even if not, they would not be prepared for the difference.
**Probably AutoCad can; same deal as Office - simple, non-interlinked files with little intelligence in the data, and a market that depends on lots of individual users at likely different versions. Forced upgrades are highly resisted.
