When a player is incapped, their health is set to… I believe 75%. I don’t believe the damage carried over to incap when you nailed the medic.
As for the rock throw on poor Hank…
Looking carefully, it seems you threw the rock at a nook, or to be more specific with it, at the part where the wall meets the ground. The rock hit the wall and ground simultaneously, creating two bursts of area damage, instantly destroying the support. As far as why his incapped state also took damage…? Hmm.
Ah-ha! It also looks like you clipped Hank with the rock as well. So he was hit by 3 rock throws because you landed the hit on the wall, ground, and hank, all simultaneously(ish). Two hits incapped him, the third hit damaged his incap health. It also makes a very cool sound, you can hear the additional impacts.
That’s my analysis anyway.