Are you talking about the walkthrough or the 3D space? Personally I think the walkthrough is better as the 3D space is kind of clunky to use.
As far as the walkthrough I would guess he used a handheld gimbal with a stabilizer and walked through at a normal rate then sped up or slowed down sections in a video editor like Premiere Pro. Premiere Pro lets you pick start and stop points so the speed up or slow down is smooth.
