時間長了亞硝酸鹽增加 --- This is NOT true. You missed author's point

As nitrite will be easily oxidized by oxygen in air  -it's a spontaneous reaction. There is not reducing agent in the air to make nitrate into nitrite, on the other hand. So there won't be more nitrite (NO2 -) in foods after storage.

The conclusion is, health problem from eating overnight foods is more likely from bacterial poisoning. It may cause diarrhea, but not cancers.