sorry for the bajej commentary but i went into the leaderboards for claire NG+ and noticed some people had a problem with this spot or staggered themselves shooting the rocketbut i hope this video help out. If anyone has any questions feel free to reach out to me :)

for anyone who runs LB NG+ this is the one rocket tech, you shot the rocket just before getting grabbed and you get taken out of the grab animation and you stagger Mr. X in the process. the bigger zombie or the zombie in the cell will grab you but that really doesn't matter.