Well, if it's a book about Napoleons march on Russia, where every German speaking nation, including Austria and Prussia, was allied to France and provided Napoleon with troops, then I dare say they are wrong.
Meh, sometimes you miss things when skim reading.
Anyways, many authors do tend to generalize the Confederation of the Rhine as "Germany" and sometimes the more ignorant ones call Prussia that name. So that might explain it.
However it is a bit weird they said they were his enemies if the book solely focused on the Russian campaign.
I think most importantly though, is that if you use the knowledge you have of the era, you should be able to figure out which books are correct and which are not, and since you're loaning and not buying it isn't a big deal if you get the wrong book, but always compare the books to eachother. That said, most books about Napoleon are decent books for information and different aspects of his life.
