That’s still far from established at the level to warrant the original expression of absolute certainty. Considering that people have been studying it for decades, and that it’s like 70% heritable, it’s unlikely that everyone missed something as simple as “they are eating too much sugar” – something like this is likely to involve multiple genetic and lifestyle risk factors. I would defer to the researchers who still characterize it as a hypothesis - for example, this article is recent but is still careful not to overstate the case:
Part of why that matters is that you will have no trouble finding people who ate little sugar and still developed it, or sweet fiends who didn’t, and presenting such a simple explanation can feel cruel to people who saw their loved ones die a pretty ugly death since it sounds like you’re saying it’s a choice.
https://www.mdpi.com/2227-9059/12/1/99
Part of why that matters is that you will have no trouble finding people who ate little sugar and still developed it, or sweet fiends who didn’t, and presenting such a simple explanation can feel cruel to people who saw their loved ones die a pretty ugly death since it sounds like you’re saying it’s a choice.