Be aware that any valid normal user account password can decrypt your hard disk—the exception being a guest account which forces the entire computer to restart into a separate, fully neutered system.
But someone at airport security turning the computer on still wouldn't have access to your user's files, presumably (?), because of user permissions - so they'd need to hack it (illegally, I expect) and why would they do that? In the context of this story aren't they just checking the serial number, presumably that's printed on the case?