And they're not being tried in those courts. Their domain has simply been seized because that's easier than winning in court.
If you are in one country, and are clearly and unambiguously doing business with someone in another country -- with written agreements, money/goods/etc. transferring -- then it's simply not a new idea that you may end up subject in some way to the laws of that other country. It also isn't a particularly scary idea.
The idea that "on the internet" is some sort of magical extra-jurisdictional space is the new and scary idea.
Non-US site, non-US registrar, non-US accounts/transactions.
Still seized by DHS. Because it's illegal in the US. That means you can be put on trial in any country in the world if you break any laws, anywhere. That's what the article is getting at.