Also, 777 ECL checklists can inhibited or modified when the aircraft senses it is on the ground. Boeing appear to have chosen not to do this with the ANTI-ICE ON checklist; maybe this is an omission/error on their part, or maybe it’s deliberate?
As far as TAT and OAT goes, if you’re not moving very fast through the air, they are practically equivalent. Even at 100kts there is ~1C difference. If a system can measure TAT within acceptable tolerances (see above post) when at 0kts on the runway, then it can do it everywhere else on the ground and it is effectively OAT.