Bonus X comes from any shot to the bumpers. He probably just played bumpers all day for a while, starting from Doctor 1. Shooting the video mode hole spots two letters in ESCAPE when Doctor 1 is active, so it's only 3 lucky bumper shots to light the Video Mode.
Completing a Video Mode spots a doctor, so you'll eventually get Doctor 6 for Playfield X. Once you get that you go to town on Video Mode with 4x active, and cream it.
85x means he made 84 shots to the bumpers ... still fewer shots than going crazy on WHO loops or sonic booms! I've never really played the game much that way ... not very exciting! But it's effective for points, it seems!