I agree that actually measuring his IQ would have been a dodgy idea, but there was no doubt he was a unicorn. He himself never made any claims about it. It was just something you realized about him after a while.
The main thing I want to add is that using IQ to quantify intelligence at the top end of the scale is scientifically bogus and in my opinion harmful because it validates depressed / insecure / chronically online people who use their "160 IQ" as a way to put down other people or to peddle pseudo-scientific nonsense. Those people often need genuine psychiatric help and (in my opinion) such validation only harms them.
I'm sure that Hal Finney was exceptionally smart, though. :)
I would have had a lot less trouble with Quantum Mechanics if I'd realized that nobody understands it, it's just that the math works. I thought it was just me that thought it was crazy.