The packet can send numbers higher than 99,999 (believe it's 18 bits, which would be 262,143 damage max.. too lazy to confirm). The 99,999 cap must be applied to individual actions, perhaps lunge isn't subject to it because they didn't consider the possibility of a 99,999 lunge.
You get one hit per runes expended, so this may have actually been 2-3 individual hits, all calculated into a single damage amount. Barrage acts the same way. I have gotten a 151k Barrage on Matamata.