It would seem reasonable that the cabin crew directed pax to stay on the wing rather than enter the water. If you look carefully at the pictures there are actually people in the slides as well as on the wing.
Perhaps at that point the pax felt safer on a more 'solid' surface such as the wing.
Usually arrows are painted on the wing surface to direct pax to the off-wing slide, as per other similar aircraft. I did have a photo somewhere but can't find it at the moment.
Edit: the arrows can clearly been seen in this link:
Photos: Airbus A320-211 Aircraft Pictures | Airliners.net