Sensing light is distinguished from seeing in the first sentence of the abstract:

>>Almost all animals can sense light, but only those with spatial vision can ‘‘see.’’

Indeed, it seems like a pretty subtle distinction. Given sufficiently bright light, sunflowers would certainly pass the behavioral experiment done here (which is very nicely summarized in Figure 1 of the paper).

The distinction must be in the ability of these starfish to resolve objects (with an angular resolution between 30-50 degrees apparently).

You could argue photosynthesis is a crude form of vision.