Tether can and has frozen certain funds due illegal activity (at the request of 'authorities') - so I've heard at least - so it would appear that there's precedent. The fact that the Feds are calling this out is... interesting if they're not also actually making any attempt to freeze these funds.

Potential dog whistling.

I would offer a different point of view. On US soil they seem to be more concerned about it. When someone blows themselves up the US doesn't get involved. When terrorist/freedom fighters attack governments with unfriendly countries the US might be funding that.

The US cares about the overall goal of regional stability. They can use terrorism by funding groups with similar interests to advance their goals. When terrorism is used against them personally they care.