[allendoerfer]

The grandparent might just be German using a literal translation. In German, it is pretty common to call Americans "US-Amerikaner", even when we are not talking shit about you.

The shit-talking is by the way something you should not take too serious. I have seen it directed at Germany from smaller European countries as well. It is just natural to target the bigger, more powerful neighbour, especially when he behaves a bit too full of himself.

Just think of Don Draper answering to "I feeld bad for you!" with "I don't think about you at all."