If you know where the BRZ ECU is located (yes,
inside the car and under the dash--So, driving through a massive thunderstorm can do no harm to the ECU as no water from the outside can get to the ECU) and if you know how wet the inside of the windshield and the dash can get during the tinting process.
It is hard to explain but if you ever see the process of applying tint film on to the windshield then the possibility is possible.
Look at minute 18 till 26. At T25 minute, you can see the tinting guy is squeezing the solution down into and under the dashboard and that's where the ECU is located. If you look closely at your car, there is a gap between the inside of the windshield and the top of the dash, where it meets the windshield.
Overall, I'm not judging that the tint shop is the culprit, but, however, tinting job can be one of the possibilities....It may be fine for other cars as the ECU may not be located under the dash, but for 86/BRZ, it's something that we have to take as a precaution.