At a fixed pressure altitude, a set amount of thrust will produce a specific Mach number (i.e. the properties of Mach account for any variance in temperature).
I can't point you towards a good reference but the sentence means that the speed of sound varies with air temperature. I think the sentence is incorrect and actually meant to say "...
properties of Mach accounted for..."
Speed of sound in air is calculated as
c = (331.5 + 0.6 T) m/s
Where T is the air temperature in degrees Celsius.