On my Android.SE profile,
top 2% this week is displayed in Reputation box:
But, when I click it, I found that my week rank is 1:
So, how does this
There were only 104 users with rep changes this week, so that works out (with rounding) to the top user being the top 2%, the text is correct.
Now, I get it. At this time situation is:
Calculating it is easy with this formula: (Rank/No. of Users with Rep Change)*100%
At the time I asked question, users with rep change were 91. After applying this formula & rounding off after considering percentile rank, it was 2%. I am attaching @balpha's comment here (which explains more):