This is a terrible article, no offense to anyone. The author literally says nothing about how to go about using "just-in-time learning." The way he vaguely describes it sounds a lot like cramming for a test.
The real world example provided - he learns to code, doesn't use it, gets a job coding and doesn't know how to code anymore. Then he says if he used "just-in-time learning" he would have waited until he needed to use the skills to learn them.
Why would you take a job that you don't have the skills to perform, and then use that time to figure out what you are supposed to be doing? Unless you are freelancing remotely and are able to bullshit your way to a finished (crappy) website, you would be exposed and fired in an actual professional environment where people know wtf they are doing.
That is terrible advice.
As an entrepreneur and self-taught designer this is exactly what I do. I recommend this type of learning to style to anyone. Would add that having a broad understanding in advance is a good idea when it comes to coding and also having someone around who's more experienced to advise.