I agree with "the commenter who spells his name with upside-down letters thereby making it needlessly difficult for others to refer to him"; I think the video guy is saying "shores up", being a spur-of-the-moment, and not particularly idiomatic way of saying that the effect in question goes away or evens out (as said upside-down-lettered guy says).
As to the intended meaning, I think it's what you, Dmytro, said, but more precisely. I think the point is that for people who are sufficiently overweight (i.e. fat) and sufficiently under-trained, and only for such people, there is a limited window of time at the start of a new regime where they can reliably and predictably both lose fat and gain muscle. However, quite quickly -- presumably as their body begins to react and attempts to regain homeostasis in various control systems -- it reaches the point where the precise extent of loss of fat versus gain of muscle is very much harder to control.
In other words, once you've reached and passed that "honeymoon" stage, you might find periods of time where you can push all the weights you want, and find that you achieve nothing but fat loss -- the usual ecto/hard-gainer problem.