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I'm not sure why it hasn't been discussed or suggested that you need to be looking at the coolant temp as well if you're trying to figure out what's going on.
As someone already mentioned, there's all kinds of factors involved in setting the target temp for the cooling system - engine load, ambient temperature, outdoor temperature. Even way back in the E39 days they had the M62TU run at a target temperature of 108C for efficiency. But, based on a dozen different things, it would lower to other target temperatures, the most extreme was 89C I think. If it was really hot out, or you were driving very aggressively with high engine loads or sustained high speed (i.e. autobahn speeds) it would lower the target temperature.
The series of engines in the F10 do all those same things, although I don't have a document on me which reviews them all (but I think I do have the N55 document somewhere).
Perhaps the 108F drive home is hot enough that the coolant target temperature lowers, thus the oil temperature also lowers?
Why don't you use the hidden cluster functions to bring up the coolant temps and see if they correlate. If they do, then you're done and the mystery is solved with measurement and facts.
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