Of course such a calculation has nothing to do with the posting situation on the forum. It is just the general probability of getting a series of n identical digits for randomly combined n-digit numbers.Imagine a more extreme case and be honest with yourself, you are receiving your ID card, and you find out that its serial number is "555555555555555555555"
ID cards are different from forum posts, because every citizen get issued only one. And 555,555,555,555,555,555,555 is different from 1,111 by multiple orders of magnitude obviously. So there is nothing to compare between noticing a member with 1111 forum posts and an ID card # with 21 consecutive identical digits.
As for honesty: Would i be immensity surprised if i got 555,555,555,555,555,555,555? Sure. Would i think that this is a notable occurrence? Yes. And not only because my countries ID cards have only 10 digit numbers.