Straight grooves have been an available option for modern trap and skeet guns for as long as I can remember...sometime referred to as "wad-lock" grooves, or wad-lock barrels...to prevent that arbitrary torsional spin of a shot column.
As far as MLs go, the only articles I've ever seen about straight grooves is that they were experiments to try and provide a place for fouling to go in a smoothbore...a bit of increased PRB accuracy was noticed...which then led to the experimentation of spiral grooves like the fletching on an arrow.
No idea if that's true but so far have never seen any other comments to the contrary...