He sort of has it right.
You can visit the past, but in doing do, you have created a new timeline going forward. You cannot return to your original timeline. The new timeline may be similar, but because so many events turn on what amounts to chance, the further back you go, the more unrecognizable your starting point will be should you ever return to it.
There is a coherent “real” timeline, we may or may not be in it, that “created” timelines either merge into at some point or branch away from entirely. What happens to those branching timelines is the stuff of fantasy and nightmares.
“in doing so” not “in doing do”
Proofreading and morning do not go together.
There is something else that is never addressed. Where we were in the past in terms of space is very different to where we are now since the earth /solar system/ galaxy and who knows what else are all in motion.