Huh, well you learn something new every day. I've seen old houses with higher breakers than 20A but they still had the same 120v type outlets, when I've seen 30A connectors listed for some RV parks I had just assumed they were 240v.
In the RV world, 30 amp service means a 120V TT-30 outlet, and 50 amp service means a 240V 14-50 outlet.
It doesn't have to make sense, that's just how they do it