My two cents--I have found that when I am taking notes from a text that I tend to duplicate the grammatical structure of the text I was taking notes on. I have to force myself to use different words. It could well be that something like that happened with your writer using the manual as a reference.
I was also told in terms of plagiarism that a text has to not be recognizable as the original text. This does take work, but it's more tedious than difficult. This includes technical stuff. It might seem there are only a few ways to say something, but there are really plenty. I did this a lot when I was ghostwriting, which was often technical and science stuff.