Yes, and it says that he consumed significantly more than before (by the way, "only" a factor of 2 compared to the plausible consumption, not a factor of 10!). Maybe some device is broken for him, heat pump perhaps running continuously in heating rod mode? Still, one should somehow come to an agreement, in the interest of future neighborhood. Maybe initially split 50/50 and after some time (and again after the next billing) take another look or something like that? If his consumption is then significantly increased again, he takes over the full amount retroactively, if not, it stays at 50/50 due to not being conclusively clear. Or something like that.