This is common. I drive and ride a bicycle a lot, so I know the area really well and rarely need a GPS for day-to-day navigation. I'll use it during rides to make sure I stay on the route for the ride, and for unusual situations (like confirming the most direct route home after a major mechanical problem). But, in general, the GPS is the backup to my knowledge.

There have been many times when a route change was proposed for some reason, and the change was laid out clearly with road names, on roads we're familiar with, and people are in agreement. But it turns out most of them have zero idea where we're talking about, and when the turn comes, they're all confused - "I thought the route went straight here!" Uh, it did, until we decided to change it at the last rest stop, as we discussed...

These are people that have been riding these roads for years or even decades. We're generally older people, too, that grew up without GPSes, so you'd think that navigation would be built in. At 49, I'm usually the youngest of the group. There's one guy - older than me - that has been riding in the area for two decades, and he does truly know every road and every port-a-pot in the area. He also doesn't use a GPS bike computer and just memorizes the routes. But most people seem to have little idea of road names or how it all fits together.

After a few incidents where confusion reigned after a course change mid-ride, I've banned "day of" route changes from rides I lead, for anything other than a serious problem - unexpected bad weather, mechanical or medical issues, road construction, etc. People just don't know what change we're making, and it causes all kinds of confusion.