Do I now actually have $300 in wealth? No, because it's illiquid, and the bid for it more broadly is likely $0, I have to apply a large liquidity discount. It seems like many communities behind these coins have been doing something similar to the internal trading I've been describing here, and hyping them to find outside people willing to trade some of their real dollars for these worthless coins, and those few trades have been used to establish the broader market caps of these things.
All illiquid and somewhat illiquid have this property to varying degrees, ranging from startup stock (no, selling 20% for $1M to a VC doesn't mean your company is actually worth $5M, unless you could find a buyer for all the stock for that much) all the way up to Amazon, Tesla, Apple, etc, because there's no buyer waiting to absorb all the outstanding stock at the current bid. There would be a buyer willing to absorb all of it at some level, but it's likely at a level far lower than the current market cap.