I double checked and the wiki is correct; the tooltip is wrong. The tooltip calculates LAND_COMBAT_ORG_ARMOR_ON_SOFT_DICE_SIZE / LAND_COMBAT_ORG_DICE_SIZE - 1 = 50%.
The code doing the actual damage calculation does 1 + <random number> mod <die size>, resulting in outcomes as @Simon_9732495 explained (2.5 and 3.5 average respectively).
But maybe the coder is wrong. The designer want +50% but the coder put it as d6 vs d4!