This is an excellent example of what can be done by a creative team that actually understands how technology works. We have a theory on how they achieved the effect... but at this point it's a guess.

We figure there's an open API that let's you choose particular keyframes that get used as playhead scrubber preview images. So, they simply edited single frames of the alternate (playhead "video") scene into the main video. And voila, anyone who fast forwards along the playhead sees the alternate... or primary message. Don't drive fast.

What do you think?