We must not expect much out of this, he gave his opinion and that is it, bitcoin returning to the previous ATH in a four year window is a reasonable prediction, so there is not much we can say there, and about bitcoin reaching 500k during the next decade, who cares? If you are a long term holder and you are planning to hold for that long then it does not matter if bitcoin reaches 200k or even 500k dollars per coin, what matters is that you will be in a better economic position than the one you are currently experimenting.
Its becoming a culture in crypto and speculation has something to do with it. Speculations are already keeping new users coming in crypto in hopes to get rich every 4 years. $68k in 4 years still is somehow high still but its happening ever after halving. The trend continues to higher ATH to higher ATH.
Given the current economy and people starting to look at BTC because they can't trust banks? $500K in the next decade is very possible.