It is I'm afraid chrome plating, not lining and I'm afraid it is NOT for protection from steel shot.I am sure he means chrome lining Brit like with the Pedersoli SXS shot guns?
As to steel shot it will not wear a barrel out but it will score one pretty bad if using steel shot without steel shot type protective shot cups. Even then you will get pin holing sometimes. Steel shot really does not belong in muzzleloaders due to the low density and high vellocity required to kill effectively with it. Can it be done, yes but the results are marginal at best due to most muzzle loading shotguns lower vellocity, i.e. under 1200 FPS.
I have used a limited amount of steel in a muzzleloader using a card wrap. A real pain in the back end to load but I did get a duck.
One day I want to test it more with higher powder charges. The reasoning being it behaves different to lead through chokes, generally wants to spread less so I wonder if through a cylinder bore it will not get a blown pattern to at least with a high pellet count be of some use over average muzzleloader shotgun distances.