About half of the study participants were non-vegetarian, IIUC. I wonder if they found any correlation after slicing by vegetarianism?

A core part of the scientific method is that you attempt to isolate a single variable at a time. If anything, all this suggests is that this was a better diet-controlled sample population for measuring the correlation of eggs and Alzheimer's than the general public. That said, the methodology of this study does not allow for inferring a relationship between Alzheimer's and meat consumption in either direction.

Adventists are okay with meat as long as it’s kosher generally.

I think the bigger factor is that they’re teetotalers.

My data points, though: two of my vegetarian teetotaling Adventist family members died of Alzheimer’s. The lifestyle is clearly not a cheat code for defeating dementia.