1. He's definitively bad at investing. He doesn't have an investment strategy, and probably never heard of portfolio re-balancing.
2. He got in lucky and made some good returns. Now he thinks he is a genius because of that, and as a result can predict the next market move.
3. He didn't do good market research. For example, most of the volume in USDT is faked by the exchanges. Coinbase, GBTC, and CME each one of these is are probably bigger than USDT in size and volume. Unregulated derivatives are an alternative to USDT for more sophisticated traders and they are also huge.
4.USDT is now also used outside of the crypto-market. Not because it is great, but because of the practicality. This offshore unregulated market of USD is worth in the $ trillions. USDT having a market cap of a dozen billions is really peanuts. That being said, I'd be more interested in an investigative journalism on how Tether has succeeded in moving such amounts of money while avoiding all the KYC bonanza a regular joe (or business) has to go through.