It's still a guessing game as the BitMEX article itself states:
...our analysis itself is weak and there is no perfect way of approaching this problem.
And later on in the article:
It is therefore impossible to do an accurate allocation. As a result, our analysis is far from perfect and we used a variety of methods, including statistical analysis, random number generators and even manual review to allocate some blocks.
So both Sergio's estimate as BitMEX's estimate are educated guesses. More certainty could only come when coins get spent..