This statement very literally means "the oldest example we currently have". When they say "in the written record" or something, that qualification is important. They're probably not suggesting that this is the first time anyone ever said it. But it's the first time we have.

This is a very common problem with etymology and historical language studies. Because they rest almost entirely on those written records, and don't have other sources like archeology we can use for general history, you have to just go with whatever the oldest example you have is. But in many cases with language, it's almost certainly not the first time someone used a given word or phrase or spelling, because usually it's already established before someone chooses to write it down and what are the chances of getting the absolute oldest example?

The same principle is true when studying something like agricultural techniques or recipes. Chances are by the time it's written down someone was already been doing it. And how could you ever be sure you've got the first writing either? You can't, but you go with what you have. When you deal with historical evidence, which is very much a pile of leftovers and remnants, you always have to be clear-headed and honest about the limitations of your sources. You don't always have the sources you would like to clarify all the details, and you can't always trust your sources either. I think a little like detective work, you have to be skeptical and you have to work as much in possibilities and interpretations as in clear facts.