Some people get upset very easily by taking something as being more serious and pointed than it really is. This seems to be yet another example of an overreaction to a harmless communication printed on a t-shirt.

By the way, which airline was he flying when this happened? Qantas. Not exactly surprised given it's the flag carrier of a country that has willfully bought into the WOT nonsense and even been blacklisting its own citizens from getting passports despite no trial and conviction of the Australian citizens it blacklists for international travel purposes.