They always count from 00 onwards with a leading 0, though (x.01, ... x.09, x.10 etc.).
The equivalent in the more common versioning scheme would be 2.8.0 which would then also be called 2.8.
Well their scheme does leave some questions open: Does 3.00 need to come after 2.99 or can there be a 2.100? Or if its more like 2.8.x: Can ever be a x.x.10? (we are talking here more about the scheme that actual blender releases)
How I currently understand is its just 2 numbers and 2.8 is a simplification for meaning 2.8x.
[1] https://code.blender.org/2018/11/blender-2-8-beta/