https://globalnews.ca/news/11080371/canadian-woman-detained-ice-example-immigration-border/
It doesn't outright say she was doing something illegal. But it does state she was working on her own business, another article mentioned it as well, that she was investing, feel free to use your non-american search engine of choice to find more. And that's not what TN visa is for. I can imagine it would be easily abused (and likely is) by investing in your own business and sponsoring yourself, if the amount you invested isn't enough to get you through the threshold for investor visa - which has been increased recently.
Multiple lawyers are quoted suggesting it was not a good idea to do what she did, one of them directly advising her, and hat she wouldn't have had the same issue at Canada border, that just screams arrogance to me.
I'm not defending what US did here, but it's like with boycotting US products....oh suddenly shopping in all those big corporation shops in Canada is fine as long as they fuck us over with Canadian products? It's gotten real quiet about that real quick. Assholes can be on both sides, just different sizes, doesn't mean you must support either.
Considering the design, I wonder if they perhaps knew from some of their euro friends that "skap" is a slang for "die" in at least a couple of central European languages