He says it's generally cultural appropriation when the events are done poorly/inaccurately, are highly Americanized, and clearly not well-researched. Based on the associated drinking culture, Oktoberfest tends to be a bit of a shit show. If an Oktoberfest is just an excuse for people to get smashed on shitty American beer while dressing in cheap knock-offs of traditional German clothes whose history they don't understand, it's appropriation. If the beer that is served is made in the German style (only water, malted barley, hops, and yeast allowed as ingredients), and the attendants either refrain from wearing the traditional garb or wear properly-made items while knowing and respecting the origins behind it, that would be different.

Fun fact: Most "typical" German outfits like Dirndls are traditional only in Bavaria (a state in the south of Germany). Every region of Germany has its own traditional dress. He says he would be satisfied with a German-themed US festival it didn't turn into a Bavaria-fest like they all seem to, but if the garb worn instead represented several different areas of Germany.