This article is light on a lot of details, I'd be cautious about believing this in any significant way. Taxi driving in London is known to have a heavy cognitive load because of the training and skill required. Where I live taxi and rideshare services now rely exclusively on software for route finding. But even in London the causality may run the opposite way - without exceptional hippocampal function you may not be able to become a taxi driver. So the activity is not necessarily neuroprotective, but the selection process may weed out vulnerable people.

Secondly the odds ratio is not impressive here. The non-taxi groups get Alzheimer's at a rate of 1.66%. the taxi groups get it at 1%. So this not a stochastic difference, just a decrease in the rate. I'm on vacation so I'll leave it to someone else to look up the study numbers and punch them into a calculator.

Also of interest is the occupational definition of how long someone needs to be a "taxi driver" to be classified that way. If someone has declining cognitive performance they may be streamed into another occupation before retirement or diagnosis. And so on.

Wait... You can die from Alzheimers?