This is what I was thinking. We've always been a species that has had to navigate, whether it's large distances, or even if in settlements, we would still have to navigate trails and pathways and get around, and know our surroundings.
Might be interesting to compare the rates of people who hike frequently, or mountain bike (both require memorizing trail systems, somewhat similar to our species previous lifestyles.) Even FPS games like Doom might trigger this.
I'm not super close with a lot of riders, but I have been in the same riding communities for 20+ years, and while I hear about people having various health issues, other degenerative diseases, passing away, etc, I don't think Alzheimer's is one I ever hear of.
Conversely, I wonder if they'd find higher rates among sedentary people, who hardly leave the house/work, or only ever travel short distances.