No, he is not in step.
Yes, he is aware he isn't in step.
Like many other really experienced DIs, he is able to walk or run around the platoon, have a conversation, make corrections, and manage to give good cadence and keep the unit in step. This is way harder than it looks. It's pretty much a flex. He most definitely would not march like that in a ceremony. The Marines marching in the platoon had a great time for sure. This is not formal. It is not ceremonial drill. For those of you who have served, especially Marines, you remember your DI giving cadence, walking backwards, or far behind the platoon to check alignment and arm swing amongst many other corrections. Your DI was not in step or at the POA. When you are preparing for a ceremony, the Drill Master is marching the battalion, often times walking at his own pace and looking at the unit to perfect the drill. He knows he isn't marching... you cannot have clean, crisp drill if you only focus on yourself as the unit leader. The purpose of this was simply to have a good time taking the Marines to eat and giving them good cadence to stay in step with.