After I was back, my water was 75 oC hot and temperature measured on board was 90. Thankfully, S9 shutted down itself after going above 90oC. Thanks to immersion nothing wrong happend AT ALL to the device or house
The tank and water were just a bit hot I don't think that proves that immersion cooling saved the day.
As you say, the miner shut itself down, as it should.
To test this, you could submerge a heating element in the fluid and put the max power which the power supply can produce through the heating element.That would simulate the miner NOT shutting down, but shorting out completely and using all the available power to generate heat.
Maybe you would have ended up with a water heater explosion? See Mythbusters experiments: https://youtu.be/rGWmONHipVo
Another question is at what temperature will your cooling fluid start to smoke and when will it catch fire like a cooking oil fire?
My guess is that submersion reduces the fire risk frequency, but if you were to ever get a fire, then it would be an instant monster that cannot be extinguished with water.
https://www.youtube.com/watch?v=3LWYXJvU7yM