Note how there is no actual substance to the classification as "fallacy". In general, it only makes sense if it condemned some absolute claim that "anything natural is better than anything man made". But people appealing to nature rarely if ever claim that - even when they appear to be making that argument, it's because they generalize.

What they actually mean is that something natural will tend to be better - and there's nuance about why that might be so (having benefitted from evolutionary pressure and adaptation, a thing empirically tested and shown working, more effortessly fitting to our biology, and so on). Of course we're talking of man-made stuff thus-far, not some futuristic utopia where we know how to make everything better.

So unless the claim is "all natural things are always better", it's doubtful how the "fallacy" accusation actually applies in real life arguments. Does it address the claim that "X is better _because_ it is natural"? Well, doesn't that being the case or not, depend on the quality of the specific non-natural alternatives to X?

If those aren't any good, then X is indeed better not by chance, but precisely because it's natural. That is, because it had millions of years to evolve, millenia to be used and tested by humans, and so on, and it had all sort of evolutionary pressures to improve it.