Very little history is taught in our high schools anymore. They might hit a few minutes of WW1 and WW2 and in both wars the teaching is mostly how the USA won both wars all by themselves, with only a little help from other countries. That is what almost all the war movies show as well. The French just letting the Germans walk into Paris unopposed in WW2 is the real nail in the coffin.
They don't teach how without the French we would not have won independence when we did, and that the French are really not cowards. There are many jokes of buying an French or Egyptian army rifle that was little used, only dropped once.
In the end, it is just a joke. Maybe rude, but a joke.