Salaries aren't in that range generally in South East Asia, where I gather the author is from.
He basically ripped off a github repo curated list of APIs and made it "searchable" + listed to PH then sold the site based on the traffic from that one spike. Not belittling it at all - he had the initiative to build it, monetize it, and sell it.
After he had the idea for tweet jobs, he said the original buyer submitted another offer on the original project (which it sounds like he had most abandoned).
That’s pretty much across the board.
Even in London that would possibly be the case, it's just the way the market is.