Criticizing the fact of the email is punishing a good deed.

Countries change their entry requirements all the time and travelers bear the brunt of it because it is 100% the traveler's responsibility to be properly documented.

We all live with it and there is no substitute for routinely checking requirements. One need not trawl consular websites as IATA's TIMATIC presents the data in a useable format and is what the carriers rely on.

As others note, this issue is much less about what CBP would do, but much more about what BA will do prior to boarding.