Yes. And if those citizens are living away from US soil (such as in Europe or Asia) they still come under that part of US law which forbids them from doing certain things. If the US agencies were so sure Tornado Cash was laundering money they should put forward evidence to their international partners asking them to do the same but as far as I have been reading they have not.
Some analysts are saying arresting one of the
alleged developers of Tornado Cash in Europe is sending out a signal the agencies can come after anybody involved in the creation and upkeep of mixers not just the owners. We are now moving in to new territory with agencies vs mixers and it is only going to escalate.
Right now as far as I understand, only American citizens are not allowed to use Tornado Cash which is a strange decision as they are also accusing it of laundering over $7 billion but that sounds ludicrous when it has passed around $7.6 billion in total.
That's partially because the US government can only pass laws relating to their own citizens - it can't make arbitrary decisions on behalf of other countries.