My guess is it's one of Joyetech's infamous control knobs. They come up with some pretty unusual switches and I'd say that one rotates left and right similar to the control ring on their previous eVics
Oh god yeah I just noticed that it doesn't have any other buttons besides fire!
Oh jesus, mod manufacturers! I thought it was bad enough that no mod maker will consider adding more than three buttons, such that we end up with ridiculous UIs like on the DNA 40 + clones (five-clicks-to-lock-then-hold-up-down-and-fire-for-five-seconds-then-use-up-or-down-then-five-clicks-to-unlock-then-spin-around-once-twice-three-times-while-tapping-out-"please"-"kill-"me"-in-morse-code-with-your-feet.)
Now they're even removing the two buttons we had? Because why have three buttons, when you could a button and a knob! Hell, why even have those? Voice controlled mods! "Up. Up. Up. Up. Up. Up. Up. Up. Down. Fire. Fire. FIREEEEEEEEEEEEEE"
Might be a tad hard to tell it to fire while sucking in vapour, of course. I know, have a voice memo feature so you can record your voice saying "Fire", then press a button to play back the recording of "Fire", so the mod can listen to that and start firing!
Hell, that'd still make more sense than Yihi using a gravity sensor for changing watts