The grey "alumina" granules are also called aluminum(III) oxide. It reacts with lye, produces sodium aluminate and releases hydrogen. The pressure and heat from the reaction helps unclog drain pipes.

Sodium aluminate is corrosive and bad for lungs. It should not migrate to the naphtha layer in theory, but in practice it is easy to pick up some water during naphtha pulls. Your lye may also contain various contaminants, possibly toxic, possibly carcinogenic, since it was not made for human consumption, and naphtha may pick up some of them.

If you do not want to switch to dryteks - try to obtain reagent-grade, food-grade, or at least "99% pure" lye.
Also, drop some of your naphtha onto a piece of glass and see if it evaporates cleanly leaving no residue. If you can get heptane (n-Heptane, "Bestine" ) - use it instead of naphtha, as naphtha contains some neurotoxic hexane.

You also used a lid that probably had a plasticizer layer. Such lids may release phthalates into your solution.

In the video you linked the dude pours water into lye. That is a bad idea.