Given the weights of the shot load in that article, they must be talking about steel shot. Steel deforms less than the buffered, plated lead shot I usually shoot. I have never shot heavier-than-lead shells, so I can't comment on performance of such (I've always been scared it might mess up my barrel). Still,at higher velocities, it seems to me like shot might not hold together well after it leaves the shot cup. By the time the shot & cup have separated, it may not matter much. Those Federal flite-control wads certainly help hold a pattern together, especially out of an older fixed choke shotgun...but they are not pushing over that ~1,300 f.p.s. number either. There has to be a reason for it.
There is a physics/ ballistics question here that I don't know the answer to. Perhaps the good people at Remington can enlighten me. I don't know anybody over there to ask, but I'm sure they have an "FAQ" section on their website. If I find anything earth-shattering from them, I'll post it.
Luck Counts, good or bad