I think they were actually talking about the data access pattern, with mergeSort you get nice sequential access to the arrays of course.
I don’t actually know how data was fed into card based systems, I mean I know they fed the cards in, but I assumed the bulk data was read from tapes or something and cards mostly held the programs. Maybe not though, it is all quite a bit before my time!
That combination isn't very common. But I wouldn't be surprised if somebody invented it 2 or 3 millennia ago either.