FTX said: "Don't worry we have collateral ... lol jk!"
SBF's parents said: "Don't worry we have collateral ... lol jk!(?)"
Your bit about "but fiat isn't real either" is true to some extent, and you could even go deeper and argue that nothing is real because we don't know if the universe is real or whatever. But honestly, in a practical context, there's a huge difference between:
I have 100 million in the bank; source: bank statement.
and
I think I have 100 million in the bank; source: trust me.