But that is a very different thing, you are talking about IOTA/USD but in fact, it is "iota/tether" And tether is a cryptocurrency, he is talking about buying using fiat.
Anyway for IOTA I can only see MIOTA/USD at Bitfinex and Exrates. you can use Tether at OKEx.
And no, there is no way to buy iota directly with fiat, you first need to buy bitcoin, and then convert those bitcoins to tether, or just deposit those bitcoins on bitfinex or any other exchange.
By this way you are able to buy iota, but directly with fiat is almost impossible.