If you read the linked Kahneman article, it actually addresses your comment. It's like the stock market: some percentage of traders will get lucky, and inevitably they will attribute their success to their judgment.
No, wasting yet more years of your life sitting in classrooms does not confer the ability to predict the future. What does confer that ability, is being lucky enough to be handed a series of projects where the hard parts are relevantly similar to your previous projects and, fortunately, nothing went very wrong on the novel parts. And it's great that it worked out for you that way, but that doesn't mean the OP was wrong.
While some people attribute their luck in the stock market to skill, it is still possible for someone to have actual skill in making money in the stock market. Some high-profile billionaires and numerous quants have demonstrated this. The fact that you made money doesn't mean your income is solely, or even primarily, attributable to luck.
Likewise, it's possible the grandparent has been lucky that the projects they've forecasted aligned well with their areas of knowledge and hit no problematic snags. It's also possible, however, that one can develop the ability to make mostly-correct predictions about project timelines. Being a rarity doesn't mean it's flat-out impossible, or even unbelievably improbable.
No, wasting yet more years of your life sitting in classrooms does not confer the ability to predict the future. What does confer that ability, is being lucky enough to be handed a series of projects where the hard parts are relevantly similar to your previous projects and, fortunately, nothing went very wrong on the novel parts. And it's great that it worked out for you that way, but that doesn't mean the OP was wrong.