The flower does look a lot like a thistle, no stickers tho huh. Still a real pretty flower, I can see why they get used as ornamentals then go feral. I wonder if that's the case of the one in your pic?
We have a new thistle that is really taking over the pastures here called russian thistle. Makes canadian thistle look manageable.
My dads favorite torture for us kids when he'd run out of other things for us to do was go cut down the bull thistles in the pastures.