The preferred temperature of bass is somewhere in the mid 80's. That said there are many different factors that could push fish out of the ideal temp. Availability of food, shelter, oxygen, and avoidance of fishing/boating pressure. A fish in 40 degree water is going to make some sacrifices to find warmer water but a fish in 70 degree water might very well prioritize proximity to prey over warmer water. It's also worth noting the preferred temp of most bait fish is well lower than the preferred temp of bass.

The book this came from is very wrong and it's been updated multiple times over the years.

It varies greatly, depending on the strain of bass and where they live. The fish in the south prefer warm temps. But the northern strain bass and the ones living at a more northern latitude are more active at MUCH colder temps. Most of the lakes in the northern 1/3rd of the country never even get into the 80s and guys catch bass just fine up there. That facacta knowing bass book is terrible, all of the studies are skewed. I read half of it before I had to stop. The guys running the tests never followed proper scientific method. Read some into it, it's ridiculous.