If the temperature of the ATF was too high, the temp light would stay on solid, until the temperature became cool enough at which point the light would turn off.
If it is continuously flashing than there is another problem.
With 4EATs, the AT TEMP light will come on after one ignition cycle to when the original problem had started. So you might feel a problem with the transmission and the AT TEMP light will not come on until the ECU/TCU sees one ignition cycle after the problem occurs, then the light will flash.
Only 2 trouble codes are generated as soon as the problem occurs which will set off your check engine light, which in your case has not happened. The other trouble codes will only trip a CEL if the ECU and TCU see the same problem happen if it has 2 consecutive faulty trips/drives. If you have one faulty trip, and then a successful/clean trip, the previous problem will be reset and the monitors reset.
I wouldn't worry about it. It might be hard to recreate the same problem if you don't have 2 consecutive faulty trips, at which point would trip a CEL and give you the code. You could always bring it to the Subaru dealer and have them check out stored codes in the TCU and then go from there.