It seems to me that's kind of the defining feature of a simulation. If there's no one behind it, if it just exists entirely on its own, then it is the natural universe, not a simulation. Even if it looks computationally-based, that's just The Unreasonable Effectiveness of Mathematics at work.
A simulation means "someone made it". They may not be masterminding details of our lives, or our civilization, or even our solar system if they only happen to care about something completely different from that and incomprehensible to us, but nevertheless calling it a simulation implies that a creator at least exists.
You are just pulling that concept from the traditional definition of "simulation", but there is no particular justification for doing so.
If we detect evidence of what the author of the paper is calling a "simulation" (that is, our universe is being simulated in a 'meta-universe'), then we know only one thing about the meta-universe: It can simulate ours. We don't know that it supports some sort of "life" of it's own, contains anything with "intent", or contains anything like that at all. We do not know that there are meta-men in the meta-universe.
Perhaps there better terminology for such implications than saying a 'meta universe is simulating our universe', but the fact that we are using that terminology in the meantime does not mean it is reasonable to make the assumptions about it that you are making. Just because we call our universe a "simulation" does not mean that there must therefore be meta-men.
(Also I do not understand the point you are trying to make about it being the "natural universe". If some sort of meta-man made a simulation that we live in, instead of the simulation arising through non-deliberate means in the meta-universe, is his meta-universe any less "natural"? Either way the meta-universe is "natural"; whether meta-men exist or not)
In a nutshell what I am saying is that we should not assume intent unless there is evidence for intent. Evidence for 'simulation' itself should not be misconstrued as evidence for intent; it would be evidence for nothing but 'simulation' itself.
A simulation means "someone made it". They may not be masterminding details of our lives, or our civilization, or even our solar system if they only happen to care about something completely different from that and incomprehensible to us, but nevertheless calling it a simulation implies that a creator at least exists.