[maytc]

That example is probably in the training data?

The puzzle assumes that the room temperature is greater than the cold milk's temperature. When I added that the room temperature is, say, -10 °C, Mercury fails to see the difference.

[djrj477dhsnv]

Under any reasonable assumptions for the size and shape of the cup, the amount of coffee, the makeup of the air, etc., the room being -10c won't change the result.

It would only matter if the air were able to cool the coffee to a temperature less than that of the milk in under 2 minutes.