As long as he isn't preaching or giving religious bias throughout the book, I wouldn't get upset about who he wants to thank. It's his acknowledgements section and he should be able to thank whoever he wants in it.
One the one hand, he's certainly within his rights to put anything in his book that he wants, presuming the publishers will publish it as is.
On the other hand, that he did indeed put that in there and in a TECHNICAL document would at least for me lower my appraisal both of the author and the contents of the book insofar as the contents' credibility and/or reliability are concerned.
It may be that he is expert in whatever field is the topic of this tome. That he indulges in such an overt anachronistic display does him no favors from where I sit.
I have a book with such an entry in it on a .net language. One of the other two authors thanked HIS partner. Now if they could get along enough to co author a book then why should I get petty about it. If the technical reference is accurate then let things be.