I think I figured out a better way of framing my gripe.

My right over property may not be natural in the sense that a force in nature can sweep it all away leaving me with nothing - IOW, it can be untied by forces other than ill-meaning humans.

However, my right to live peacefully on and to use my own property without unjust interference is, probably, natural, because no earthly creature has a better claim to what is mine.

Now, I haven't entirely worked out what happens if an alien civilization comes and lays its claim to my bitcoin through some unknowable power. In this case, perhaps, I will reconsider what is natural