I think knowing precisely how it is worked out is less important than just being aware that it’s a general ‘average’ figure and that most individuals actual usage will vary due to several factors such as:
How warm you like your house, occupancy time, insulation levels, age/efficiency of boiler, how good your windows are and whether you shut your curtains at night, are you in or out of the house a lot
What your mix of gas/electric is, eg are you cooking, showering and heating on gas or electricity
How often are you washing your clothes and towels and how are you drying them
Do you have lots of gadgets, gaming PCs, big TVs etc et
Any specialist medical equipment or more frequent washing/bathing needs than average
Anything less common like hot tubs or fish/reptiles
Etc etc
But if you use above average and you’re 2 people in a small house, it should be clear that you might have scope to reduce your usage, but if your house is large, detached and has 5+ occupants, maybe not.
Also the ‘benchmark’ of the price cap amount and your bills are well below that, it’s an indicator that you probably can’t reduce it much further and if you’re in any way vulnerable, it might be a prompt to seek help if you can’t afford a more comfortable heating level.