The big thing is the amount of energy required to make a glass bottle, which would be fine if it could be reused enough times. But the available figures showed otherwise.I'm sure you are right...I'm just finding it very very hard to believe if I'm honest. Sounds a lot like one of those sponsored "research projects" which basically sets out to prove something that benefits the organisation paying for the research.
Surely most plastic bottles basically end up being environmentally negative....vs glass which is inert.
Actually, here's a link to the research summary - https://earth.org/glass-bottles-environmental-impact/
(original study was done by the University of Southampton, but I can't find a more detailed summary just now)