Using that service has gotten many posts killed, many accounts banned, and many sites blacklisted. Just because people are selling upvotes doesn't mean the buyers are actually getting onto the front page with them.
The votes on the OP look legit to me. Perhaps people were reacting just to the title and perhaps skimming the readme. That's a different kind of problem.
> After seeing that link yesterday where you could buy Hackernews upvotes,
This is much harder to pull off more than once than you might think. Keep in mind that everyone who votes must have an account and HN has complete visibility to every user’s voting history, karma, etc. It’s not foolproof, but detecting votes by low/no karma users is not rocket science.
The votes on the OP look legit to me. Perhaps people were reacting just to the title and perhaps skimming the readme. That's a different kind of problem.