This is a weird "vehicle" called the Flyrad. It's essentially a set of handles attached to a motorized wheel that you hang onto and get dragged around on. They call it a unicycle, but that seems inaccurate as you need to be wearing rollerblades of some sort. Otherwise it'd be like getting dragged behind a boat but on pavement instead of water, which seems awful.
In addition to getting pulled behind this thing, you can also flip it around and sit on it, still using your rollerblades as wheels. It is very strange! It's supposed to be released at some point next year, at which point I'm sure you can expect to see people everywhere tooling around on these weird things.