Correlation isn't causation, but causation usually comes with at least a little correlation.
This looked at breast and colon cancer, which could be drowned out by noise from other cancers if this doesn't apply to them, for one. Other sources of cancer like diet, smoking, and being constantly irradiated would vary on a national level.
Also, the post seems focused on cancer becoming metastatic, which wouldn't be the same as cancer incidence, and looking at cancer deaths isn't helpful either because of variations in treatment, etc.
Increased urbanization, increased consumption of processed foods (drastically), increased stress levels, decreased sleep levels . . . the list just goes on for changes.
Then you have to question the quality of medical autopsies performed in the '70s and the examiners ability to determine cause of death. Then you have to question the causes of deaths and if there truly has been an increase.