More like the initial design concept was defined over a weekend. The actual detailed design, even for highly successful programs like the F-117, took much longer. Nobody ever designed an aircraft for serial production over a weekend, not even back when planes were build out of canvas and wood.
EDIT: After reading the article, what Boeing did back then was the same thing as Boom coming up with a rendering and a high level design concept over the weekend. Also, back then times, and technology, were different.
I think the point being made is that many projects start as an idea that is then brought into the prototype phase, iterated upon, and then is complete whenever the project delivers a significant increase in current capabilities compared to the current systems.
This in contrast to the F-35 project which apparently decided all the capabilities up front and then has went about designing an aircraft to somehow reach all those goals. Whether or not it will is a subject of ongoing debate. It also somehow has wound up making 3 different airframes.
A good example of this would be Soviet copies of the B-29 & the V-2. In both cases there was pressure to "build our own that is better". Apparently Stalin got involved in both cases and demanded that a way be found to produce a domestic copy first, then learn from that, & produce a domestic design next. Not sure how accurate that is, but it seems to have worked out. Soviet long range bombers & Soviet missile systems are certainly nothing to scoff at.
EDIT: After reading the article, what Boeing did back then was the same thing as Boom coming up with a rendering and a high level design concept over the weekend. Also, back then times, and technology, were different.