Yeah pretty much. General purpose compression algorithms do a good job but pale in comparison to what Roaring achieves.

I wouldn't use the word exotic but rather specialized and/or optimized.

Infact later versions of Roaring use run-length-encoding (RLE) containers in addition to array and bitmap containers which is a technique shared with more traditional/general compression algorithms.

In effect rather than achieving "very good" compression, Roaring is very close to "optimal" compression for sparse bitmaps.