the idea behind some traditional medicines is treating diseases with opposite of what caused them. Diseases that came from cold, are treated with heat.
Which is why the vast majority of folk remedies are ineffectual, as they are based on, in a lot of cases, superstition and nonsense and in most cases deliver either no benefit or no benefit over and above the placebo effect. Those that have been shown to be efficacious have been integrated into medicine. Aspirin, which I have previously mentioned, is one such case.
Artemisinin is another. Then they are properly packaged, marked, delivered in carefully controlled doses with "use-by" dates. This is in marked contrast to many "folk" remedies where there is little or no control over potency, cleanliness of preparation or age. Modern medicine, allied with access to better sanitation , is the reason why life expectancies across the world have increased from
31 years (early 20th Century) to 67 by 2010.
The farcical idea that diseases are treated "opposite of what caused them" is probably related to the ideas that originated with Hippocrates, who tried to treat mania with small doses of Mandrake root, as a large dose causes mania. The phrase "hair of the dog that bit you" derives from this. It's snake-oil of the highest order, and one that Hahnemann perfected into the bull-turd that is homoeopathy.
And as for claiming that flu is caused by cold? Rubbish.
I also had the flu once. I have never felt so sick before or since. Even my skin ached, which was a first for me. It developed into a proper chest infection that had me in bed for 5 days, allied with a raging fever that caused pretty freaky hallucinations.