I'm skeptical of the methodology and explanation as presented in this article, but similar things have been observed in the academic literature.
The most famous one I can think of is the pre-FOMC announcement drift (https://www.newyorkfed.org/medialibrary/media/research/staff...). The authors observe that "80% of annual realized excess stock returns since 1994" are accounted for by the 24 hours of trading before an FOMC announcement. If we take this as evidence that the Fed "causes" most of the stock market's move (which we probably shouldn't), the effect is nothing new.