In the GameXplain interview with Dickhiskhan, he explained that the footage the Switch trailer was added post-production. They were holding dummy units with high security making sure that the actors stuck to the plan. Dickhiskhan also told that they played some Splatoon on Wii U beforehand, so that they could mimic the moves on the Switch controllers.
In response, Eurogamer asked a Nintendo UK spokesperson to comment on the matter. Their response was the following:
"This video is all about explaining how the Nintendo Switch works. We wanted to convey in a self-contained video how Nintendo Switch represents a new era for video game systems enjoyed in front of a TV, by letting gamers play anywhere, anytime, with anyone they choose. It adds the mobility of a portable system to the power of a home gaming system.
At a later date, before the March launch, we'll be talking about things like exact launch date, and of course, the games. You shouldn't assume what you saw on the video represents actual game footage and further specifics on first-party games will be provided later."