That is correct.
For matrices that distance is treated as the operator norm. By definition, for matrix m this is the maximum value, among all vectors v of Chebyshev norm 1, of ||m.v||. Since we can make every element of v have absolute value of 1, this is seen to be that maximum row sum of absolute values.
This might in general be a better question for a math forum, by the way. It's not specific to Mathematica.
