iPhone XS Max water resistant?

Hi.

I know that my iPhone XS Max has IP68 that gives the device to be under 1.5 m for 30 minutes.

So few days ago I was stuck in a heavy rain and I took out my phone to record it while running in the rain. Used it for like 1 minute under the rain and put it in the pocket.

After the rain I took the phone out of the pocket, the phone was still wet a little bit, was using it and in suddenly the phone shut down.

after few seconds the apple logo showed up and after 2-3 second the phone restarted and like that non stop - the phone didn’t work.

So so I went buying some rice and before putting it in the rice, the phone turned on.

But still wanted to put the phone in rice, so turned off the phone and put it in the rice for like 5-6 hours.

After pulling out the phone, turned it on, the phone restarted for like 3-4 times, but it did turned on eventually.

After some use, notices that the proximity sensor didn’t work and the screen wasn’t so bright even in the max brightness.

Decided to bring the phone to lab to fix it. They checked it and told me that after they opened the phone. There was NO ANY SIGN TO WATER inside the phone. They closed the phone and EVERYTHING WORKED!

so what do you think was the problem?