Yes you are correct.
No, he isn’t, gravity assist is Orbit Mechanics 101.
Textbook crap that was first thought up by the Ukrainian mathematical physicist Kondratyuk.
Been done a bunch of times by NASA and other operators.
https://en.wikipedia.org/wiki/Gravity_assist#Historical_origins
But don’t let facts get in your way, Genius.
PS: this technique was also depicted in the movie “The Martian” when the original mother ship needed to get back into Martian orbit when it was almost back to Earth and out of propellant.