Isn't this the classic Five Eyes loophole? I'll spy on you, you'll spy on me, and we'll exchange notes.
So how is this the "classic Five Eyes loophole"?
Although the US ANOM data wasn't sent to the FBI, presumably a foreign agency could see that data and tell the FBI which US citizens might be involved in illegal activity so they can be monitored/investigated in other ways.
Homeland Security specifically promises to delete any data once they've finished, but it doesn't say anything about the agencies that they presumably share it with.
Basically if the US wants data on particular people from the Five Eyes network, it can be arranged. And once it's in Langley, it can go anywhere.