Is it because it has SECR marked rakes? That can happen many times when another zone supplies the rake due to lack of coaches. Or in this case, the plan might be to have SECR take over the train once GC is complete and to have WCR handle the train for now and SECR may have accordingly provided the rake.
Cases of trains not following the numbering are rare in IR. As the number indicates, there might be some arrangements in the background because of which the numbering is given as a WCR train.