50 Amp Outlet Disconnect Requirements
Inspector is drunk.
The cord/socket is the disconnect device
The purpose of a disconnect switch, or a locking device on the breaker, is so that a craft or trade can “lockout/tagout” the equipment while it is being serviced or maintained.
There have been too many cases of Goober knowing where his machine’s breaker is, walking the 2nd floor and noticing his breaker is off, turning it back on, and then shocking the repairman on the 3rd floor who is (unknown to Goober) servicing the machine.      Since Goober is on the 2nd floor and the machine is on the 3rd, Goober does not have line-of-sight to the machine and can’t see the repair cart and worker.  If there was line-of-sight from panel to machine, the disconnect would not be needed.
However, this scenario presumes a hardwired machine.  When the machine is cord-and-plug connected, the service person is expected to simply unplug it.
So there is no earthly reason for a disconnect switch on a plug-in machine.  In fact there’s good reason to cord-and-plug connect a machine specifically to avoid the need for a disconnect.