This isn't a real thing, I've never heard anyone say "thousands of grams" in my whole life.
When people (and I mean, usually law enforcement) want to inflate the numbers on drug busts, they convert it to "doses" at some unknown conversion rate, or to "market value". Which kinda makes some sense, because it takes into account the purity level, but still sounds weird.
Concentrate like that is usually sold by the gram. I'm going to assume they phrased it like that so we stoners can immediately visualize it as 3000 1g pots.