It's funny, because by the same logic, I could argue that 'Bitcoin is a stablecoin, since BTC1 = BTC1'.
Not exactly, because they are comparing 1 dollar with all other fiat currencies and with other assets like gold, silver, etc. to determine how stable dollar is.
I don't think that's how stablecoins are defined. The definition of 'stable' is 'when measured against USD'. Just like they measure stocks and other assets against the USD; they do so with cryptocurrency and if a currency is more 'similar' to the US dollar, it's called 'more stable'. But I argue that the dollar itself isn't stable, and I don't think anyone doubts that.
Stablecoins are cryptocurrencies where the price is designed to be pegged to a cryptocurrency, fiat money, or to exchange-traded commodities (such as precious metals or industrial metals).
Basically,
peg = stable - which is pretty misleading, if we look at the USD purchasing power chart.