from the wikipedia on the book a grandmaster used it to learn chess "Grandmaster Maurice Ashley has said that Bobby Fischer Teaches Chess was his first chess book" there can be a whole lot more grandmasters that learned from the book
"Bobby Fischer Teaches Chess" is a good very first chess book for someone who knows nothing or very little about chess. It was my first chess book as well. In fact, consider that every chess player, including GM's, knew nothing about chess before they learned anything about the game.
it was written by expert teachers after all. wikipedia quotes bobby about his teacher
"Mr. Nigro was possibly not the best player in the world, but he was a very good teacher." – Bobby Fischer
can we vice versa say
"Mr. Fisher was possibly not the best teacher in the world, but he was a very good player"
Fischer was a top class writer and teacher.
bobby fisher teaches chess has often been recommended for kids and beginners but was it written by bob or not we may never know.
I some times drop in the forums just to talk about fischer, as a matter of fact he did write " bobby fischer teaches chess" He says so himself,
https://www.youtube.com/watch?v=rS9n-8bmhV0&t=3484s&ab_channel=chessinkino
at 22:48
"i wrote the book, bobby fischer teaches chess." - bobby fischer