Blowing things up
Tim may downplay the "blowing things up" economic growth during the war - after all if we produce billions in bombs and other military infrastructure that is either destroyed during the war or has greatly reduced utility after the war, that part of GDP is simply a mirage.
However, all the civil infrastructure that is damaged or destroyed and needs to be replaced, while having a bit of the 'broken windows fallacy' about it, still needed replacement after the war. So you had much of Europe needing to rebuild that infrastructure, and less damaged countries providing the industrial products to aid it. Thus the growth in Europe fixing/rebuilding things, and the growth in the US supplying a lot of the manufactured goods to help that effort.
While the US didn't have the damage Europe did from the war, consumer spending had slowed greatly, to only the necessities. Factories that had produced cars, radios, and whatever had converted to producing tanks, military radios and so on. The population had been buying war bonds with their surplus income instead of spending it on that stuff. Once the factories went back to consumer products, there was a lot of pent up demand and a lot of savings to spend on it. Though this probably only accounts until the early to mid 50s in the US.