I must admit that I can't see a motor, but I have some reservations about him riding unpowered.
His cadence looks to be too low and more in line with somebody riding an electric bike. My cadence on my road bike is about 75, but if I want to pass somebody or shake them off, it goes right up to about 100. He clearly seems to be concerned about you following him, like he's trying to shake you off, but his cadence stays steady like mine does when I'm on my electric bike at around the limit of assistance. It just doesn't look right.
Secondly, that pack on his waist looks very suspicious. Unfortunately, the photo isn't clear enough to see if there's a wire going down the seatpost.
Thirdly, in my experience, people that can pedal at 20 mph, normally have better bikes.
Lastly, it looks a lot like a throttle next to his hand, though it could be a grip-shifter.
He hasn't got a hub-motor, neither a Bafang BBS or similar, but there's still a few other crank motors that could be hidden in that photo.
I'm not saying that he has got a motor, but I wouldn't write off the possibility.