I lost my phone in the mountains and it was under the rain for a day. Next day I found it. First thing I did was to remove the battery, no even testing if it was working as it can destroy the phone.
Then when I came down to civilization I put it in a tupperware covered by rice. I left it there together with the battery (out of the device) for the whole night (around 12 hs). Next day I turn it on and it has been working since then.
The problem that you describe looks like it has not dried completely. Heating it up is does not seem an amazing idea for me although 50º is not a massive temperature it is possible that some condensation evaporated but never managed to escape the device or screen.
Using a hair dryer is also dangerous for several reasons (check the link at the end).
In my last trip I have recovered with rice three different devices with just a bag and rice: a camera, a watch and my FairPhone.