I thought the author did a good job describing how he rationalized away these warning signals as flakiness, and had a bad mental model of the situation ("SIM card is being weird") that prevented him taking timely action. He also mentioned outside factors (needing to sleep, stress at work) that affected his judgement.
It's easy to say this would never happen to you, but even sophisticated people get caught by this stuff, since we are in the end human. Writing this article in the aftermath of losing so much money was a brave and considerate gesture.