FFF-
re: your edit. Actually, I think you had it right the first time. He says the OAT is -25C. The ISA deviation would be approx. -40, but the OAT is -25 and that's what you enter the chart with, not the ISA deviation.
Splitting hairs, but assuming a standard lapse rate, it makes little difference if the reported temp from the airport is -25, or if the OAT guage in the a/c is reading -25