Earlier quoted context omitted.
What triggered this investigation? I agree that it does look like a phase-change. But did you throw out any graphs that didn't have a phase-change appearance? I'm genuinely curious. Seems like there are different arguments below-the-surface in this thread.
For me, what triggered it was noticing several startling graphs that all seemed to show a) something sudden, b) at the same time. I started collecting such graphs. It appears the author of this website has done the same. Note that all the "commentary" is embedded in the images - there's no indication that the webmaster has any agenda beyond mine (although the various graph publishers might). I don't really understand…
Unrelated in what sense? Your example seems a bit of a straw man. What other graphs of economic activity and change do not show a significant and sudden shift at ~1971 (is what I think the parent is asking)?