Though technically not a wrong statement, just the wording is misrepresentative.
In fact, out of all the searchs online, you will find this quote.
"Since 1971, U.S. citizens have been able to utilize Federal Reserve Notes as the only form of money that for the first time had no currency with any gold or silver backing. This is where you get the saying that U.S. dollars are backed by the ***“full faith and credit” ***of the U.S. Government"
Pretty much most countries today no longer have a quantifiable ITEM to back their currencies, except china, which their currency is still backed by gold. Its an argument inducing Conversation really.
But really, the US currency is essentially supported or BACKED by its countries DEBT.