I knew a 5-year old that was not much below 5' tall, and built like a linebacker (hefty, but solid). Ended up being just slightly above average height when full grown. Kids are weird.
The officer thought the same thing apparently.
"At first, he thought the boy appeared to be 8 or 9 years old."
Heh, I remember being ~6 and thinking they had an age limit for driving "so you'd be big enough to operate it", but then I figured that couldn't be right because I'd seen little old ladies that were about the size of some 10 year olds.
When my Grandmother pulled up in her car, it looked like there was nobody driving. She wasn't tall enough for her head to be visible in the windshield. I don't know how she saw anything.
My nephew is only 3 and bigger than some 6 year olds, he's massive. He could just come from a tall family.
It's a small car by US standards, and the kid is wearing a sweatshirt that's incredibly baggy, along with shorts that are oversized-enough to be swim trunks. The seat is also reclined. There's a lot of optical-illusion going into the presentation there. It's actually pretty clever.