Because there's nothing in the article. It's a couple loosely correlated events around '35-'55 that anyone can Google together in 10 minutes. The article has no more authority that anyone's post around here.
My bet is still WW2. The fact that the boom started earlier than '45 is easily explained by his own quoted graph in which the birthrate plummets in the 20s (which I would assign to WW1), the first rise is merely a correction.
Why would one result in a bust and the other into a boom? For one, the economy followed the same bust ('29) boom pattern. WW1 ended unresolved, showed the evil of man in general, where WW2 resolved WW1 and showed the evil of particular man, and it wasn't us, but which we defeated.
WW2 learned a lot of lessons from WW1 which made post war society thrive for not only the rich.