Quoting the description of Junkrat’s Level 1 Talent “Bouncy Bouncy”:
“Upon colliding with terrain for the first time, Frag Launcher grenades deal 20% more damage.”
This talent only works when you bounce grenades off objects protruding from the ground, for example a wall.
Bouncing grenades off the ground itself will not increase the damage.
Either that is a bug or the talent description direly needs to be addressed, as the ground would commonly be understood as “terrain” and should count for the talent.
Various definitions of the word “terrain” are “a tract of land”, “a piece of land”, “a geographic area”, etc etc, using “ground” as a synonym for the word.
Terrain in this game refers only to walls or surfaces that a hero cannot normally walk through
The ground itself does not qualify for this
This same logic is used for Diablo’s Shadow Charge and Hanzo’s Scatter Arrow
You will notice lines around walls and certain objects when you come close to them while playing these heroes
This is an indication that they qualify as Terrain for the purposes of abilities that utilize them
The ground not qualifying as Terrain in this game is intentional not a bug