Its not so much a misinterpretation if you look at the question asked, though agree that it is very much a stretch.
Poster was looking for some general constitutional support for putting the breaks on this sort of FinCEN abuse, and there isn't much there on this matter.
What sort of FinCEN abuse? What specifically have they done that violates someone's rights?
If you want a constitutional challenge, there would need to be something specific that you have a right to do, that FinCEN told you that you can't do.