The appearance of nicotine in Egyptian mummies is easily accounted for because of its presence in food items the Egyptians used, as well as tobacco-based insecticides many museums (from which the mummy samples were taken) during the 19th century. The presence of THC in Egyptian mummies isn't mysterious at all, because cannibis is indigenous to the region - the Egyptians used it to make rope, and it's also known that the burning of incense produces THC in small amounts which can add up when inhaled over time.
In fact, the only difficult-to-account-for finding is the presence of cocaine in the Egyptian mummies. However, it isn't suggestive of trans-atlantic travel; any plant of the genus Erythroxylum produces cocaine, and several of these plants are present in southern Africa and Asia, particularly India. Lapis Lazuli - a stone native to Afghanistan - has been found in some Egyptian tombs, indicating trade with those areas.
If we are to accept the existence of a trans-Atlantic trade route between the Egyptians and South America, we need better evidence than chemical residues which can be accounted for otherwise. It seems almost humorous that such a route could be established, but the only things the societies traded with each other were recreational drugs.