Uh I mean, maybe not officially but there's a whole lot of precedent that if you engage in trade using USD that you're under US jurisdiction.

Really. How valid is that? If an American tourist uses 20USD to pay for a meal in Montreal or Toronto (which happens a lot), what's the logic that this falls under US jurisdiction.

If it's true, I'd avoid USD like plague

Yes, you should avoid USD like plague. That's why Iran and South Korea established payment facility denominated in won, South Korean currency.

https://www.rt.com/business/443354-iran-south-korea-currenci...

I mean, it's obviously valid because this incident happened (and many other events that show the same validity). The logic is that the US says any transactions involving USD fall under US jurisdiction, because it's their currency--that is, the USD only has any value at all because the US government says it's legal tender.

Because the USD is the international reserve currency for a lot of countries and the US largely is pretty stable, most countries are fine with cooperating in cases like this with notable exceptions.

FWIW that's changing under Trump (i.e. people are seeing the US as less stable), and the EU is making efforts to increase the use of the Euro as an international reserve currency.