Not a horn antenna, more like just a fat ground plane. In the side view the bottom part should be attached to the coax braid and the top cone to the center conductor. The ground plane is angled away to reduce capacitance from the fat driven element. Since its multiband the angled driven element probably helps to keep the radiation more consistent over multiple bands kind of line a bicone but its not big enough with respect to the various cell bands to be a bicone. The wire bridging the two pieces would keep the driven element grounded and its probably at some strategic point where it doesn't look like a short to RF.
