I think the article was interesting, peoples comments more so...
Re: Canadian Flag...old news certainly, but I still hear people in the US suggesting doing so, it has become a "thing". Now usually it is from those that do not travel, or much, and it seems to come and go with the political state, several years ago, in to 2016 timeframe, for several years it seemed to be a thing again...not sure why.
Re: Being spoken to in German, in Germany. Well, makes sense, that is the language. But more so, German is the largest ancestry group in the US...so many of us just have German and European traits. But mostly, among my German acquaintances, I find them to be pretty direct, and what I experience is you will be addressed in German, until you correct them or request to speak English. The exception will be in very tourist type places. Now being addressed in German in Greece, Italy, or Spain, then yeah, maybe more your appearance.
Re: Clothes; I think the salient point about clothing is less the specifics of what you are wearing, than if it is situation appropriate. I think back a few years ago when outdoor clothing became the travel rage (hey, it is lightweight, weather proof, comfortable) my European colleagues started commenting about all the Americans going on "safari" while visiting the city. Yes wear what you want, I just cringe thinking of the public Walmart pajama wearing trend being exported to Europe.
But above all it is the interpersonal things that resonate with me, as I have heard them before from my European colleagues. One guy who visited the US was just shocked that while standing in line with a guy that he went on about his job, all his health problems, family issues, you name it, all in the course of 10 minutes or so, and added that Americans tend to share too much, even discussing your job, not including work situation, is something many Europeans do not chit-chat about except with good friends.
Also received comments that while it is good to learn a few basic phrases, using the equivalent of please and thank-you multiple times in an interaction seems strange and insincere. I have noticed that locals, more in Spain and Italy, use voice inflection to indicate both please and thank-you, rather than saying it often, Hard to explain, but a well inflected "Ciao" can express "Thanks, Goodbye, and see you soon" at the end of an interaction.