I think Saylor is more correct than wrong.
Bitcoin is more than a currency and is fundermentally backed by "nothing" like fiat.
That is unless you see Bitcoin itself as the asset itself like gold. Meaning it doesn't need to be backed by anything.
Now as to why property, I would say it's easier to understand property. Digital asset is akin to collectibles in some sense.
But his largest argument why it isn't a competition to USD, is there's no need to call it one to have extra threats and frankly there's a bigger market. Same way Satoshi thought it was too early for Bitcoin to be used for Wikileaks.
Bitcoin once big enough will be much harder to stop. People will then find their use case of Bitcoin.