It is quite possible this spray wouldn't work for the reasons you mentioned, but there are a couple of things you missed which I believe warrant a study:
This spray is not an epoxy. As stated in the article, this spray adheres to virtually any surface in a layer which is 15-30 atoms thick. This implies to me that it has an extremely high wetting ability which may act to draw it into a crack. It is clear in some cases that capillary action can be stronger than atmospheric pressure for some substances. This is clearly not the case for any sort of epoxy. It's possible this spray is so wet that it would in fact be sucked into the crack, but have minimal impact on the sharpness of the crack. It's also possible that it would adhere well to the crack and have a substantial blunting effect. It's unclear how this spray would interact with the large particles left in the crack.
As I said, it's quite possible this spray wouldn't be useful in this application, but it is a big mistake to think that what you know about how epoxies are used to repair windshield cracks has anything to do with how this spray would react. Further study might be quite interesting.