Great story headline, extremely poor content. He reveals very little about how he came up with his guess. All you are left with are just obvious statements:

Here, my costs were negative—it was an interesting and fun problem to consider and even small projects are opportunities to teach and improve—and the upside was positive. Why not make a bet?

I'm really not interested in learning when you should make a prediction; I'm more interested in learning how you make the best prediction. In the end, I am left disappointed.

In absence of much explanation about how you reached your predictions, it sounds like you just picked a number off your gut since you had nothing to lose.