Bitcoin market cap values are calculated in the terms of dollar or other fiat currencies but it doesn't means that fiat money is involved in the crypto fieldthe prices were just based on satoshi and one bitcoin will be always equal to one bitcoin.
Marketcap gives very little indication of much fiat has actually changed hands.
Let's say I want to go and buy 10 bitcoins. I go to my favorite exchange, and put down a buy order of 10 bitcoins. I buy the first sell order at the current price ($3,800). Then I buy the next sell order at a few cents higher. And then the next sell order a few cents higher than that. And so on and so on until all the sell orders combined reach my total of 10 bitcoins. All in, I'll pay more than $38,000, because each subsequent sell order is more expensive. Let's say the final sell order was at $3,900. This means that somewhere between $38,000 and $39,000 has changed hands. However, given that the final sell order was $100 more than the first, I've just increased the marketcap of bitcoin by $1.75 billion (17.5 million coins * $100 per coin). An increase in marketcap of almost $2 billion has been achieved by spending less than $40,000.
I think that is why about 50 billion dollars or so is involved in bitcoins system, that's not crypto though, crypto probably has over 100 billion easily, this is just bitcoin.
My example above becomes even more ridiculous when you consider altcoins. I can create an altcoin with 1 billion tokens in circulation and then sell a single token for $1 to my friend. My altcoin would now have a one billion dollar marketcap despite only one dollar changing hands.
