The company made an offer. The person accepted it. Nothing notable about the scope of the work changed (at least as detailed in the blog post). The person wasn't stiffed or otherwise cheated. They just... didn't like a job offer which they themselves accepted.

" I told them that amount may work and went on with my day."

I don't read that as accepting the offer, I read it as continuing the negotiation.

I absolutely read that as accepting the offer. If you say that an amount "may work" then well, that's it, they are not going to increase the offer unless you ask. The next sentence confirms that too:

" 6 days later I was told that the doubling was approved and we could sort out the fine details "

Like ok, we're now past the payment negotiation stage, now onto other details.

The person in the article clearly(to me) agreed to an insuficient amount of money, and then wrote a blog post to complain about it.