He probably had to in order to match the small amount of voltage coming from the laptop. I would bet a decent amount of money that signal was distorted.Look closely at the end of the video how far he turns the gain back down looked like he had it maxed out to me.
You would figure they'd done a trial run before the "live performance" to tweak things properly and make sure everything was good to go. There's certainly nothing wrong with doing things adhoc, but in that case, expect the unexpected.He probably had to in order to match the small amount of voltage coming from the laptop. I would bet a decent amount of money that signal was distorted.