Sounds like existing law is being enforced under Trump that wasn't enforced when Obama was President. Hello! It's. The. Law. Obama not enforcing it doesn't repeal that law. IOW, the outfit who organized these students' trip F'ed up. Not that facts matter on DU.
Now, you want to talk about shifting standards, different countries recognize passports in their final year differently. Some refuse to accept a passport that is within 3 months of expiring, other countries won't accept when it's within 6 months of expiring. Some countries change their "standard" without notice. Welcome to real life.