No I think what they mean was that we did not discover (or the Japanese, rather) that we have separate receptors on our tongues for umami until fairly recently. We knew what it was, but didn't have a proper name for it.

No, they clearly meant that umami wasn't recognized as the fifth taste until recently.

But never mind that; I just want to chime in that garum (fish sauce) has been a thing in the west since ancient Roman times, if not earlier.

I recommend the Tasting History videos about it, BTW:

1. https://www.youtube.com/watch?v=5S7Bb0Qg-oE
2. https://www.youtube.com/watch?v=ICZww0DtQKk
3. https://www.youtube.com/watch?v=woTh70WZ6ao

I mean, you quoted the line and missed the last two words as umami. That's absurd, it's right there to see.

Up until the term umami spread outside of Japan, nobody called the flavor that. And it still took longer before people figured out that it was its own taste in the same wau sour, bitter, salty, and sweet are; that it has distinct receptors.

Before that, there wasn't really a specific term in use. When people referred to what is now called umami, the vocabulary was different. Savory and meaty are the two I remember being most used, and they have other usages for food. Savory is very often just used as an antonym for sweet, and meaty just means "meat like" without drawing a distinction between the saltiness and slight metallic tang of meat from the part that is umami.

I don't know how old you are, so you may or may not have been around during the spread of the term and its eventual discovery of having its own receptors. But it was "viral" in the way it initially crept in, then exploded as every cooking show started talking about it and familiarity with the term spread. There was a collective "ohhhhhh! That's what I've been experiencing", and the word got adopted. Now it's a part of the collective lexicon.