This says 80% of the knockback, 100% of the hitstun. Its definitely not extra hitstun though. It is less knockback. I don't know how you would test that, any PMDT member should know.
However, hitstun is proportional to knockback, which is why you can guess when people will be out of hitstun based on how their trajectory looks like, but meteor ground bounces throw people off. In Melee the hitstun formula is 0.4*knockback, I'm guessing it's the same in PM.
So in the end I'm guessing the reason I remembered 1.3 is this :
say you were hit by a meteor with x knockback while you're on the floor. You receive 0.8 * x knockback in the end, but receive 0.4 * x frames of hitstun
say now you were hit by a move that sends you upwards, with 0.8 * x knockback. Then you'll have the exact same trajectory as you had for the meteor, but you will receive 0.8 * 0.4 * x = 0.32 * x frames of hitstun
0.4/0.32 = 1.25
Therefore, you receive 25% more hitstun if you were hit by a meteor compared to the same trajectory without the ground bounce.
...
Which is my very long and elaborate way to say that yeah I probably just misread it a couple months back and won't admit I'm stupid.