That was my read on it anyway, that the gum absorbs the mercury that is in mouth/gums/saliva some of which is leaked via chewing.
This is how they list the product in their catalogue:
"Another unique product formulated by world chelation expert, Dr. Garry Gordon. This pleasant orange tasting chewing gum contains EDTA to specifically help remove heavy metals from inside the mouth. Chew after meals and discard once the flavor has gone knowing that you are removing mercury and other metals from your mouth and gums"