To call those antennas "stacked" is BS. When you stack antennas you mount two or four identical antennas either vertically or horizontally. You do this to either gain signal strength or to increase the increase directivity of the antenna to reduce multipath or ghosting. All antennas must be pointed in the same direction and connected with the exact same length of coax cable from the antenna input to the combiner(which is simply a hybrid splitter).

That link is just for a VHF antenna and a UHF antenna mountted on the same pole.