I feel like talking about this because it cracks me up.
That guard right there is Nash, who, as far as I know, stole a uniform and was also spying in the Highland camp at the same time as Riou and Jowy.
He gets stuck guarding the provisions and then these two show up.
So, Nash probably thinks Riou and Jowy are in the army, while they certainly think the same of him. Spies spying on spies. The Highland Army was chock-full of spies and they had absolutely no idea, at least not until Rowd recognizes them.
Which means poor Jillia had her tent invaded by spies seeking shelter twice in one night.