The topic is sharing culture, where lots of very patriotic US things have their origins in other cultures. How so much of the US identity is a mish mash of other cultures. The US is even known as a cultural melting pot!

The hypocrisy is being ok with other cultures if you're familiar with them, but hating 'new' culture. The comic is criticizing xenophobia by pointing out the (somewhat) xenophilic history of US culture.