He's absolutely right. In order to make a copyright claim to a list of facts (such as the average MCAT of every medical school in the AAMC), they would need to claim some sort of creative originality in how those facts were selected and organized (
http://www.bitlaw.com/copyright/obtaining.html#compilation). If the selection criterion is "Is the school in the AAMC" and the organization is "alphabetical order", I really don't see how they have a legal leg to stand on. It's settled American law that the whitepages, for example, are not copyrightable, because they merely provide an alphabetical list of names and phone numbers of every resident of a certain area. The Supreme Court has ruled (
http://en.wikipedia.org/wiki/Feist_v._Rural) that because this doesn't require any originality or creativity, it does not enjoy copyright protection.
I understand that studentdoctor doesn't have the legal resources to fight bull**** like this, and that furthermore they would like to stay on the good side of the AAMC, so they're unlikely to fight it. That's fine. But the fact remains that any legal threats AAMC is issuing are empty on their face. Their legal department appears to be full of scumbags. It's disappointing that the AAMC isn't a more ethical organization.
To summarize, no, you shouldn't worry about the legal repercussions of passing around this excel file. There are none. The only people who could support a copyright claim to it are the people who prepared to excel file, not the AAMC.