Yes, one of several buses on loan to assist with COP work. It'll allow the deckers to go for contract and other service work.
List according to bustimes:
https://bustimes.org/operators/stagecoach-west-scotland/vehicles
SL64 JBO (10420) - On loan from Stagecoach Manchester
SN66 WAU (10806) - On loan from Stagecoach East
SN66 WBD (10807) - On loan from Stagecoach East
SK19 EWH (11215) - On loan from Stagecoach Cumbria & North Lancs
SN69 ZGB (11266), SN69 ZGC (11267), SN69 ZGD (11268), SN69 ZGE (11269), SK20 AWO (11533), SK20 AWZ (11541) - On loan from Stagecoach Manchester
SF08 GOC (25219) - On loan from Stagecoach Cumbria & North Lancs
SF13 FMZ (25265) - On loan from Stagecoach Cumbria & North Lancs
All of the above are Enviro 400 MMCs, with the exception of 25219 and 25265 which are Optare Versas.
It may have been 25219 you seen as that has been running services out of Cumbernauld.
Ironic how 25219 and 25265 have returned home in a sense, with the SF plates indicating they were new to Western.