Circuit breakers in "ordinary" boxes
What you may be seeing is a flush-mount version of a spa panel or enclosed breaker

From your description, I would reckon that what you are looking at is something akin to a "spa panel" disconnect or circuit breaker enclosure, only in a flush-mounted configuration (vs. the surface mounting typically attributed to spa panels and enclosed breakers).  These are usually 2-4 space loadcenters, with 70A to 125A bussing; larger versions use a breaker with line and load lugs instead, bolted to the box, and are called enclosed circuit breakers.