There is a minimum quantity for almost everything classed as a hazardous material before it is restricted or regulated. Among those for which any quantity is regulated is class a explosives and certain radioactive materials. No a couple of 18650 lithium batteries aren’t being classed and treated as hazmat. FAA and Homeland Security came up with the laundry list of items deemed prohibited for checked and/or carry on luggage. Funny though how a person could get right on a plane nowadays with a taser disguised as a vape mod. They strain at a gnat and swallow a camel the saying goes.
I’d say it’s 50/50. Some of the mods generate incredible current. Maybe baggage scans have been catching more and more vaping devices, as vaping use has increased. I’m sure the airlines or TSA keep track of suspicious xray hits in luggage. Vapers are bringing half their collection with them, on vacation. Someone noticed, and imposed the hazmat rule, on them.
Passenger(s) complained, maybe caught the ear of a human interest news bit. Someone in the anti vaping community saw the potential ammo, and ran with it.
There ‘is’ a safety issue, but haters gonna hate, and use the bad press.
I understand what you’re saying, and as a ‘general’ rule, in ground, air cargo , and air charter shipments, those rules apply.
Commercial passenger aircraft, are a different duck, rule-wise.