Rotary engines are wankel engines, which are only used by Mazda in their cars. If the cylinders are arranged radially it's called a radial engine.
IIRC, one of the very few helicopters to have a radial motor was the Sikorsky S-58, which saw action in the Vietnam War. But generally pretty much all helicopters have turbines.
Yup, I know, it doesnt check out at all, you wouldn't put a rotary on a helicoptor. But "rotary" engines were indeed used on aircraft, since they also refer to a radial cylinder configuration where the engine housing moves and the axis is fixed. So I think it's likely they were referring to the common WWI plane engine. I didnt think of a wankel at all till you mentioned it!
Interestingly enough, modern wankel engines are also sold for helicopters.