I can't recall the hn thread (there have been tons of crypto currency threads recently), but the comment was referencing this reddit discussion where a bitfinex representative made the same conjecture:

https://archive.fo/R6sku

> Isn't it more plausible that this is not someone writing a check for tethers (money coming in from outside the crypto ecosystem) but more likely it is coming from converting other cryptos into USDT?...