Condensation will cause some water in oil. But I am not sure if it can cause significant amounts. In an engine, the condensate should not accumulate. Each cycle of heating the oil during use, should drive the previous condensation out through evaporation. I would think this trans. is either sealed, or set up the same way as an engine.
Since condensation has not been an issue for the rest of us. I think there is more to this particular situation.
It will be interesting to see if he changes the oil, and no longer has a problem.