I don't think he does....
"below -40" = COLDER than -40
i.e. -41 or colder !
However, during descent (low thrust setting) the EAI must be on in icing conditions at ANY temperature regardless of the SAT. Of course, not if the TAT is greater (warmer) than +10. This is due to the much greater incidence of icing occurring at low thrust settings.
Any clearer ?
Best regards