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Its an arse covering measure.
Tung oil in its pure form is classed as non-flammable, so can burn only at pressure or when heated. It is possible that if you buy a quick drying or a brand of tung oil that can't guarantee its purity that it has been cut or mixed with some form of linseed oil.
Attached is the safety data sheet for Liberon pure tung oil, the brand I use, and I need to know the information in it because I need to be able to show clients that it is safe for me to use in their homes (on the rare occasion that I apply finish on site).
Right thing to do wrong wood treatment. It's boiled linseed oil that can ignite rags not tung oil.