That's doesn't mean the battery heater is on. Here's a trip where the preconditioning message was on for the whole trip:
View attachment 1020456
Interestingly the state of charge doesn't drop dramatically when the heater is on.
Are you sure? I think that graph is telling us something very different from your summary.
If you look around the middle of the graph there is a section where the speed is jittering around 70mph - I'm looking around the time frame of 12:26 through to 12:40. During this time there is a section from 12:26 to 12:34 where the battery heater is off, and then a section from 12:34 to 12:40 where the heater is on.
It's a little difficult due to the granularity of the SOC graph, but I look at the graphs and see:
Period 12:26 to 12:34, SOC: 56% -> 50% so 6% drop in 8 minutes (no battery heater)
Period 12:34 to 12:40, SOC: 50% -> 43% so 7% drop in 6 minutes (with battery heater)
Assuming 75kwh battery, and same average speed:
No heater: 4.5kwh used in 8 minutes, so 0.5625kwh per minute
With heater: 5.25kwh used in 6 minutes, so 0.875kwh per minute
So around 1.5x energy usage with heater than without.
If you were averaging 300wh/mile without the heater, you'd be then getting around 465wh/mile with the heater on.
I've got a Model Y LR - and that pretty much matches with my experience of what heating the battery results in.