From what I know, the mineral oil builds are usually more for novelty than utility. Mineral oil isn’t a particularly good heat conductor, and it’s several times harder to push around than air is, so it’s not great for efficient thermals. It’s usually just done as a sort of “lol look at what I could do” build by people who have more money than sense.
The cable is probably routed outside (likely towards the roof) in a humid environment with the indoors end being at a lower pressure. At night, when the air cools, the humid air would condensate and start dripping out
I worked for a wireless ISP that had this problem with one style of dish we were using and this was the solution the engineers wanted us to take (just stripping the insulation to let water drip out before it got inside anything).
It was dumb because the POE the line was going into would very easily catch fire if water was introduced through the Ethernet cable. We had alternative dishes that we should have been swapping out for, but of course they wanted to save money instead of being safe.