In a very superficial sense I think what he is saying is "true".
Zero is "not physical real" in the same sense that any number is not.
There is no strictly "real" one apple. There is no absolute physical means of determining if there are any, or no "leopards" in a room. We have no way of verifying if a vacuum has "zero" things in it.
This of course is just silly "clever" word games which bring us no closer to deriving meaning or understanding of reality.
The purpose here, is that math, in relation to reality, is a means, a process, by which humans attempt to derive understanding of reality and should not be confused by the thing itself.
It's silly and redundant to eagerly point out, "aha,... but "x number" is not real,... see this clever hypothetical I've come up with! " because math from the start never insinuated it was any such thing at all.
The properties, qualities, states, and history of states of physically real objects which math describes for us are very much real, but the math is not this "real" itself, insofar as much real as we say a thing can be real.
That is why in the deeper sense Astrai is right.
When he says there are zero leopards in a room, he is making a very rational, and very importantly, an extremely limited logical argument. At best the only "assumption" he makes, is that we are mature enough to not require a "might as well be interpreted as / is indistinguishable too / let us agree for the argument that " to every sentence he writes.
To read into this very precise and limited statement about reality and attempt to extrapolate from there somehow this whole big mess of other unrelated declarations and assertions about all of reality that Astrai himself did not even claim, or make, to then base an entire line of argumentation on them, is being clever for the sake of being clever.
This does not helps us.
So, yes, Cap. You will not find a "1" or "0", or "5" laying around somewhere for you to pick up.
This is not a great novel transcendent observation.