[too eazy]

because the odds of him calling on the turn with TT 99 are slim, and he may elect to turn other hands like AK and randomness into bluffs on the river.

also most players will not call a bet on the turn with TT 99 but feel that the line is "fishy" given he checked the turn and call a shove on the river with the same hands.

thats my guess as to his logic anyway.