One, that's a scooter; not a moped. Depending on the model, they can have motors up to 500cc (although that one doesn't look like it's bigger than 125cc). Still, they can reach 60+ MPH.
Secondly, who knows why the rider is being chased. He may have just committed armed robbery. It must have been something serious to warrant that much attention. I happened upon a police motorcycle accident Friday night on my way home from--of all things--training local police academy cadets. Once we called 911 and told them that it was an officer down, we had 10 squad cars, four fire trucks and EMT plus a police helicopter on us in less than five minutes. Some situations will draw in all officers within range.
Lastly, this would be better placed in the 'WTF' thread; so I'm moving it there...
Cheers! M2