I dont see the breakthrough. All light causes evaporation, even at near-zero heat. Every light ray has the possibility of knocking off a molecule of water, transfering enough energy to turn it into gas. If the angles are just right, the water molecule vibrating just the right way, it gets lauched off the surface to become gas. Whether it stays gas depends on other things, but i dont see how observing the process is anything new; Better defining the process but not worthy of the article title.
'All light causes evaporation' is not really true. IR heating works because the wavelength resonates with the vibration modes of the intramolecular bonds. Water has low absorption of visible wavelengths, so you would not expect light absorption in the visible spectrum to provide enough energy to knock individual water molecules free.
Water is an interesting substance and a lot of the properties of water come from intermolecular hydrogen bonding and polarity. Even though it's a liquid, there are transient molecular structures that spontaneously occur in bulk due to hydrogen bonding between water molecules. The polarity of water causes interesting effect at interfaces (surface tension, electrical double layer, etc).
It's possible that the water in the hydrogel is forming some hydrogen bonded structure that interacts with green light. Where the individual water molecules won't strongly interact, the larger structure does. That could lead to the ejection of 'packets' of water molecules as discussed in the paper. Why and what these multi-molecular structures are? No idea. But this is a very interesting effect.