Partial quote from the article itself, which is not so out-of-context as to be false: "[... T]he Moon, [...] lacks a substantial and gaseous atmosphere like Earth’s [...]"

By comparison, the article's use of "air" is used in a more fast-and-loose manner.

Can't help thinking that there are elements of the paradox of the heap here. Taking the article's argument to an extreme, we might say that space itself isn't "airless" either because there's more than one particle per cubic metre.