I am confused about this notation for matrix representation.

Question

I am confused about this notation from the image below. How can you represent something like (1,2),1 as a 2D matrix?

For S1 = (0,1,2) and S2 = (0,1) I would expect two matrices like: [(1,0),(1,0),(1,0),(0,1),(0,1),(0,1)] and [(1,0,0),(0,1,0),(0,0,1),(1,0,0),(0,1,0),(0,0,1)]