Shags,
The story is not as black and white as what you may have been told.
The captains were indeed on a day off, but a delay to their flight occured, forcing them to stay the night at the destination instead of returning home. The next day was meant to be a day off, and as currently KA pilots are "working to rule", they didn't want to work the next morning.
I guess this is the "grey" area of the situation. My last company contract stipulated that if days off were infringed due to delays en-route of an already started shift, then we had to finish, ie: bring the plane back.
I hope it all turns out well for them.
WP