How on earth could you think the most likely option is that a human wrote that sentence on purpose? It's not the type of wrong that comes from low effort levels, it's the type of wrong that comes from not being a human.

Humans make that error all the time. They can hear the author has abruptly endings and write it down. I think this case it actually was AI (according to some other HN comment) but you don't need to be an AI to make this error.