Yes. The Reichenbach Common Cause Principle [1] tells us that behind every correlation there is a confounding variable that causally influences both of the corrrelated variables, so the project may very well be onto something.
The article already hypothesises a few confounders (leaf hair trapping particles, plants sequestering pollutants in other ways) but psychological reasons could even turn out to be stronger, given how little of exercise is sufficient to offset cadio-vascular risks - more plants around make it more likely for people to go outside for walking or running.
