Either a lot of people are (a) making typos or (b) underclocking their P-II's, it does exist.
When you see this mentioned in software requirements, they are probably confusing a Pentium-MMX with a PII, since from the applications perspective they are identical. When you see this mentioned as a dual system (i.e. the Dual PII-166 System I see as a first hit) they have probably confused it with the PPro, which was sold in 150, 166, 180, and 200MHz variants.