It seems that a reaction can appear as zero order with saturating concentrations of substrate, and if we see a non-linear rate then we have to predict what caused it, and it seems that the passage only indicated that saturating solution leads to a change in mechanism, so a non saturating solution will reverse this according to the equation in the passage. lnM=-kHT=kt
Moral of the story is not to jump to conclusions( like the mechanism is different) when they present information about the other pssibility.