Isn't the difference that a stock is only traded on a single exchange? If stocks were traded on multiple exchanges, and the value was reported as the average across all of them, then that number would be just as made up.
And things like gold or oil barrels also have multiple exchanges.
https://en.wikipedia.org/wiki/Unilever#Legal_structure
Unilever plc and Unilever N.V. ...operate as nearly as practicable as a single economic entity, whilst remaining separate legal entities with different shareholders and separate stock exchange listings
Also worth noting that for both stocks and cryptocurrencies, the price that is shown is almost always the last traded price not a quote for a price you could trade at anyway.
[1] in the US, for example: https://www.sec.gov/foia/docs/atslist.htm