Your definition is correct under international law, but that definition mainly aims to serve policies governing war, so it's not especially apt here.

Civilian in law enforcement jargon means a non-sworn position: https://www.discoverpolicing.org/explore-the-field/civilian-...

To make this more interesting, Posse Comitatus employs the language to signal "non-Federal forces" eg: National Guard activated by a state to operate domestically are referred to as "civilian law enforcement".

In any of the above cases, calling LEOs civilians would be incorrect and would eschew them of many of their responsibilities.