Effectiveness of TI (thermal imaging)

[Imp]

Hard to say from the info given but generally no though they do see better to the rear than they should due to the way the game engine works.
What range
Was the enemy tank stationary or moving, its more likely to see you & get a shot off first the slower its moving.
How fast did you move, anything over 1 hex increases chances of being spotted by a fair bit.
Was any enemy infantry on the ground near the tank to act as extra eyes. This is the best protection vs a sneak attack it will most likely fail.
You can sometimes see this work clearly as a sort of ripple effect, nearby units react.
Any further activity in the area & the words out more units will react especially in a modern game with decent radios.

Probably infantry on the ground or he just got lucky if you only moved 1 hex.