It is not a phenomenon and they are not even separate species. The so called scientists did not even bother to test whether they could produce viable offspring between them. So no, they do not show speciation.
I love predictable patterns. But be that as it may, why does it matter if they COULD mate when in a natural environment, they DON'T mate?
Take the salamanders. Please. Ha!
But seriously, I expect a hybrid between two such wildly different coloration strategies will produce offspring less fit than either of the two parents, and therefore subject to significantly greater predation than either of the parents.
In other words, even if the two subpopulations did reproduce successfully with each other, a higher mortality rate for the hybridized offpsring, and not necesarily lack of offspring would create two subpopulations reproductively isolated at the end of the ring.
I ask you this: What is the difference in reproductive success between a mating that produces no offspring, and a mating that produces offspring that are immediately eaten?