Yeah, for a brief moment, I thought it meant using lettuce in place of cabbage, which I found odd, because you'd expect them to be using lettuce in the first place. Then I realized it must mean replacing lettuce with cabbage.
Which incidentally, I generally do anyway at home. Red cabbage is crunchier and visually more appealing than bland iceberg lettuce. Plus lettuce seems to go bad much, much quicker than cabbage, which seems to last an eternity in the fridge. I've never had a head of cabbage go bad before I can get it all consumed, but I used to waste a lot of lettuce that way, to the point I quit buying it. Cabbage also has a lot more fiber, vitamins, and minerals than lettuce as well, but I mainly prefer the extra crunch.