Market capitalization is a illustration of the strength of a currency. So I can't say it is 100% correct and may be misleading sometimes. Let me give you an example,

Lets assume a coin named ABC has launched 1000 coins in the market. The coin is listed in an exchange and someone buys 1 coin with $5 price. The market cap of ABC coin will immediately become $5000 without the rest 999 coins hitting the market.

Also to your question, there is no corelation between bitcoin conversion to tether printing. So chill!