Usually when I read about "battery drain" on the forums, it refers to drain while the car is sitting. One reason this can happen, and likely the only reason, is that something continues to run when the car should be off and sleeping.
If you're talking about higher consumption while driving, that seems to me that any "drain" is likely related to physics while driving. This is because all of the systems in the car are already running.
That said, the car does have a way of running the motors inefficiently to generate heat for the battery... so I guess it's a possibility that the software could accidentally reduce efficiency while driving.
My guess is that most likely, you experienced a heavy headwind or perhaps you were driving slightly uphill. Was it raining? Is it a mountainous route?
The trip energy usage screen does a good job of explaining where the energy is going. Too late to look at it for that trip though.
