Alternatively, maybe it's a play on words. For example, "bus" as in "buttocks", but that's a stretch. Let me focus. The user might be referring to using the elbow strike (encoxada) from the top position (bus top) in a grappling scenario.
The top deck of a bus is a particularly favored space for perpetrators. Why? Because it’s often less visible to the driver, more crowded during rush hours, and offers quick escape routes via the rear stairs. Victims may freeze, thinking it’s just the movement of the bus — until they realize the pressure is intentional and persistent. encoxada in bus top