I recall that photo. I wondered if it was made by a manufacturer that sort of "adapts" their basic radiator to fit multiple cars. They may use hex plugs of varying inside diameters in order to make it work with whatever sensor the buyer's car is equipped with. I'm just guessing. Regardless, I'd be afraid to give that thing a twist also.

You know the sensor is bad so you don't have much to lose if you break it. You might be able to grab one of the spades with a pair of needle nose pliers and carefully give it a little tweak up and down to see if it's got a rubber O-ring between it and the inside of the hex plug. If it wiggles independently of the hex plug then maybe you can wiggle it around a bit while pulling it out. Can you grab each spade with a separate pair of pliers?