Tom, you might as well accept that as a positive as much as possible. They say imitation is the sincerest form of flattery. I would add "and thievery".
A couple of years I posted a long article on one of the boards I visit. Sometime later I clicked on a Google link to read up on that subject, I think using sonar to locate deep water structure, cover, bass and crappie in deep main lake waters. And No, I have yet to read a book on that subject. I saw a lot of familiarity, and suspected my wording was in there word for word. Sure enough. I pasted a paragraph in quotes in Google and came up with at least 4 additional fishing forums where I was copied verbatim, but changes were made to make it a little different, like applying to Texas lakes. I contacted one board owner who emailed back "Sue me." I researched it and learned that can't happen. Even if the article was copyrighted it nearly impossible to do a thing about it unless someone is marketing it, like in a book.
It's a different world from what the two of us grew up in. Crap went on back then too, but folks back then seemed to know right from wrong, while too many these days don't see a difference.
Anyway, that's how you confirm that is happening. In Google or any search engine type in two quote marks then paste the suspect sentence or paragraph between them. It's a high probability that even one sentence exactly matching was copied. A whole paragraph matching word for word? It ought to be inarguable court evidence.
Jim