That's pretty impressive. Worst ever in
my old Insight was 53.3mpg over a tank. That was also in cold weather, but with the IMA working!
I put it down to the battery not being in complete health, which led to it cycling more often, and because my commute was fairly short the engine spent more time trying to charge the battery than it did benefiting from assistance.
Still, I wasn't too disappointed by it either - a bad day in an Insight is still more frugal than most people's good days in other cars!