I'd think they Kludged on a set of thumbshifters off a mountain bike..
or some discontinued sun tour part, sun tour themselves is discontinued.

There is an adapter that goes in the back end of the handle bar, and offers a smaller tube ,
compatible at 7/8" to fit a grip shifter on there , designed by The Hub BuB bike shop in Ohio
so its named the hubBub adapter.

just putting on Bar end shifters seems simpler to me , but it's your project..