Seems like they found a correlation, and called it a causation.
Seems like the common trait was probably poverty. Poor people got sicker and died more, yes, and then later poor people were more attracted to political extremism and the hope that a leader could rise to make Germany great again.
Maybe fewer 'poor' people to kiss the butts of German elites (serve them) was the problem... but I'm guessing it's one of the correlation is not causation things...