I believe the oils aren't divided this way for any taxonomic reason, but rather because we already have evidence of olive, avocado, coconut etc. oils having little-to-no impact on health, in contrast to other oils. The groups are basically "presumed innocent" oils and "presumed guilty" oils.
Or, to be more charitable, the groupings can also be looked at as "oils humans evolved eating" (olive oil, butter, coconut milk, etc) vs "oils we just started eating recently, because they can't be extracted without modern technology."
Or, to be more charitable, the groupings can also be looked at as "oils humans evolved eating" (olive oil, butter, coconut milk, etc) vs "oils we just started eating recently, because they can't be extracted without modern technology."