The device was called L’Arbalete la Sauterelle Type A D’Imphy, and it quite literally was a crossbow, using the tension of two bent steel rods to provide the energy storage that sinew provided back when the Romans were building this sort of thing. A metal cup held a spherical Type 14 grenade (weight roughly 1kg/2.2lb), and a pair of hand cranks on a rack and pinion mechanism were used to cock it.

The name translates to “The crossbow the Grasshopper” according to Google translate but if any native French have a better insight it would be appreciated.

The device was designed by a French artillery officer by the name of Elie André Broca… These crossbows were actually fairly sophisticated, and Broca put together a company to manufacture them. They would turn out to be fairly well-liked by troops, and did a good job of filling the technology gap until more modern light mortars could be developed and mass produced…

https://www.forgottenweapons.com/larbalete-la-sauterelle-type-a-dimphy/

For French readers: ~~http://kaloujm.com/lance_grenade_de_tranchee.pdf~~ https://www.kalasnyikov.hu/dokumentumok/lance_grenade_de_tranchee.pdf