I don't think they were complaining about the distance per se (they damn near won their class so they were certainly capable of the 5 miles!) so much as they felt that the fact that they were simply told to walk on back to base and nothing else belied a complete lack of logistical preparation or adequate explanation. They just got the sense that there was no planning at all and the organisers were simply winging it.
I have to say that for all the rights and wrongs of the whole thing (and to me no one emerges from this episode totally blameless) the absolute lack of humility of any kind from Mike Parsons greatly mitigates my natural inclination to take the side of OMM in all this.