521 BTC is currently worth about $320,000, and not $1 million.
"without investing any fiat" makes no sense to me because you can trade BTC for fiat at any time. Stefan Molyneux currently has $320,000 worth of fiat invested in BTC. Where the $320,000 came from makes no difference. He is investing $320,000 in BTC.
i think the OP is generally asking if there are stories from holders of ~1500 btc and is only using stefans hoard as a example of someone holding more than average which may become valued at $1m in the future.
i think the OP see's stefans holdings and presumes stefan did not directly put in his own FIAT initially to buy those bitcoins. meaning stefan only received bitcoin as bitcoin, rather than being fiat rich initially to just buy $300k of bitcoin upfront.
put it this way you dont need to have had $1million dollars initially to accumulate gold which one day may be valued as $1m..