I agree, the ECU does not' 'learn' your driving style per se; but it does calculate the average fuel consumption, and that is largely affected by historic driving style (i.e. speed, terrain, distance and load).
Accordingly, it is that historic average that is used to calculate an estimate of the remaining distance that could be covered.
The ECU cannot possibly 'know' future driving style' and has no other variable to use in the calculation.
If those variables above change significantly, so will the accuracy (if one is needed) of the prediction.
As the 'history of driving', my term, is the main basis for the prediction; resetting the trip, thereby deleting the history, and starting a new history, will discount previous data and base a new calculation on the new data it will acquire over the next few miles.
I have a vehicle with two trips (as many do), and by resetting one periodically, the difference between single journey data and, say monthly or quarterly data can be compared.
It is surprising what the difference is.
I agree the remaining distance can increase,
If resetting the trip it can only increase, initially.
I use to get much amusement from increasing the remaining distance on a previous 5.3l V12 machine !
Smiles per mile until I arrived at the petrol station.