No, Big Macs are priced in many currencies, and this is used to find relative over or under-evaluations of currencies.

https://en.wikipedia.org/wiki/Big_Mac_Index

Big Macs expressed in, say, Yen, and calculated in Euro by their conversion rate, can be compared to Big Macs bought directly in Euros.

There are of course differences, which can also be partially accounted for by different *valuations* of the specific item of a Big Mac in different societies, but it gives a rather rough index of "true value of exchange".  They indicate differences on the 10-20% level or so.

Bitcoin went up from 10 000 BTC for one pizza, to about 200 pizza for 1 BTC in 7 years or so.   That's not a unit of account.  In Big Mac terms, that's 6 orders of magnitude.

It is a known economic experience that collectibles are never good units of account: it takes active steering (which can be automatic, as I said before) to keep the value of a currency more or less stable.

In fact, you can measure it in another way: if you can get genuinely rich with it by just hoarding it, it isn't a currency.  It is a speculative asset.