I don’t know where the “thusly” comes from, but I didn’t read that the Lagrange points were 120 degrees in front of and behind the larger one. I read they were in front of and behind the smaller one. Whatever.. I’m just glad there aren’t three.
Yes, that is what the text said. Draw a circle on a piece of paper. Draw points on the circle 120 degrees apart from each other. You should have three points all equidistant. No matter where you put the large body in relation to the smaller body it will be 120 from both Lagrange points.