This is literally another name for prop_physics
LINK_ENTITY_TO_CLASS( physics_prop, CPhysicsProp );
LINK_ENTITY_TO_CLASS( prop_physics, CPhysicsProp );
LINK_ENTITY_TO_CLASS( prop_physics_override, CPhysicsProp );
Not only that, but its classname is changed back to prop_physics after spawning:
if ( FClassnameIs( this, "physics_prop" ) )
SetClassname( "prop_physics" );
Why do we need an entirely different article for this, exactly?