If the torque converter seal is leaking I see no way on earth they’re responsible for this. The seal is located between the converter and the transmission. To tamper with this at all means they would have to remove the transmission from the car.
Here’s a couple of possibilities that could cause this. (assuming converter seal)
Clogged or defective transmission vent. When the fluid gets hot it expands. If the vent is inoperative fluid will try to force out somewhere.
Another could be a leaking transmission fluid cooler (inside the radiator). The cooling system is under pressure when hot, and especially if the transmission vent is faulty, maybe the cooling systme is pressuring up the transmission internally and forcing fluid out past a seal that may not normally leak.
I’ll reiterate; what you were told by dealership about being angry, standing behind it, yada, yada, yada, is bunk.
I GUARANTEE you that if a converter seal started leaking after a simple transmission fluid change they would not for one minute stand behind that for free.
Nor should they.