Does cold brew served hot taste good? I have never really considered asking for it hot before simply because I thought it would just be like regular coffee. But, I guess if regular coffee tastes different cold and hot, cold brew should too.
Showing IDs would work, but also training employees not to assume a warning is a glitch would have prevented him from boarding. If they took the time verify that the original person had already scanned their ticket, they would have noticed something was wrong.
EDIT: this is assuming that the warning is not routinely ignored (i.e. there's actually a bug in the system and it would slow down boarding time since it happens so frequently.) If that were the case... they should fix their system lol