Truss definitely gave lots of misleading statements in these interviews, and the "nobody will pay more than £2,500" is downright abysmal.
The correct terminology is Typical Domestic Consumption Values (TDCV) and they are set by Ofgem. These are for gas/electricity in kWh:
Low - 8,000/1,900
Medium -12,000/2,900
High - 17,000/4,600
You have also fell into the trap of calling these "average" - they are not - they are "typical" (Truss was actually correct when she used this term). Their real and original purpose was mainly to use for comparisons between energy suppliers.
You have also made the error of saying "By the laws of maths, half of people will pay more than the average" when it is the median that half would pay more than - the average (mean) could be higher or lower than the median (although it was actually median bills that Ofgem used when deriving the TDCVs).
The table in the picture shows actual average (mean) consumption by region. Note that only 2 regions (London & North East) use less electricity than the typical medium user, and only 3 regions (London, North Walest & South West) use less gas than the typical medium user.