TL;DR the author developed an algorithm to solve this specific problem:

> The popular Roaring Bitmap format uses arrays of 16-bit integers of size ranging from 1 to 4096. We sometimes have to check whether a value is present.

There's no claim that this algorithm is universal and performs equally well for other problems.

In fact, note how the compare operation on the data types involved (16-bit integers) is quite cheap for modern CPUs. A similar problem with strings instead of integers would get no benefits from the author's ideas and would actually fare worse, due to useless comparisons per cycle.