It calculates that figure depending on your recent driving history: so that suggests that you've just been either:
1 - doing a lot of urban stop/start driving and/or
2 - hoofing it a bit (only you know which…
).
It should recalibrate if you then start to drive it on longer runs (e.g. motorways): my wife would typically find that she could drive it for more than a hundred miles before the "remaining range" figure started to fall….
Not the most sophisticated system, but ok once you get used to its logic.