I'm a German, I spend a lot of time in the US. My US friends here seem to analyze what I do often based on my nationality ('Oh you cook, must be a German thing'

I'm a German, I spend a lot of time in the US. My US friends here seem to analyze what I do often based on my nationality ('Oh you cook, must be a German thing'). Analyzing/Interpreting people's behavior based on nationality must be an American thing.