I got to it by thinking "YBP" as "Years Before Present", and k as a thousand, like a karat. Thousand years before present. 5,000-7,000*one thousand = 5-7 million.
Don't get me wrong, I like the guy. And I'd be a massive weenie hypocrite if I called him out on every time he was insecure on the forums. The fact of the matter is, he predicts pattern progressions reasonably well, for weeks out. But his secrets shall die with him so long as he fails to find a way to translate to english.