“Glass is a liquid, after all.”
No, it’s not. If it was there wouldn’t be well-shaped glassware thousands of years old. The “old windows are thicker at bottom ‘cuz thy flowed” is BS - panes were made and installed that way back when.
I guess the proper way to phrase it is that "Glasses" are amorphous solids, that is, they don't have a regular shape.
Therefore, while they have properties in common with liquids, but are not liquids. The flow effect of glass may be observed in the lower grades of glass, but not in the higher grades of crystallized glass.
FWIW, the program did not state whether the glass fall out over time was due to any flow or simply a deterioration over time of the grout, sealants or whatever was holding the glass in place or of the glass itself. It was simply my assumption. Sorry.