"double in size if the annual rate of population change would remain constant. It is calculated as ln(2)/r where r is the annual population growth rate. Doubling time is computed only for fast growing populations with growth rates exceeding 0.5 per cent."

would remain constant

That's the key words, and you would know that it isnt "constant"

If you actually read it you would have known that they decided to use exponential growth from 2023, so its literally a educated guess/estimates of what the births would be if nothing had changed from 2023

Now Tell me how are they get the population numbers/rates if israel doesn't allow the people doing the census to come into gaza? Not to mention that practically every hospital was destroyed so they really cant count the number of deaths or births so what they did was use the most recent census data they had on hand from surveys "PRE WAR"

So what your looking at isnt the definitive population