Smitten

The guy waving looked like a camper/hiker to me. Notice all his gear? He was probably just waving to call attention to himself and his gear - "don't run me over". Or maybe he was just lonely. Either way you don't normally hitch a lift on a dirt bike, escpecially carrying all that gear.

I was referring to the guy waving at 1:17, but he probably just lives nearby.

Hitchhikers? On a road that is clearly closed to traffic? I think you mean hikers.

the waterfall at the end was pretty

The Japanese text with the YT video says this is a part of the "old national highway No. 222", near Miyakojono in Miyazaki Prefecture. (Google Translate is your friend.)

It's not surprising either. The mountains of Japan are full of old roads and trails like this. When a landslide destroys a large piece of a road, they just build a new one elsewhere.

(Don't bother looking this up on English Wikipedia, the articles about the Japanese road system are poorly written and lacking in references. BTW, did you know that all the major divided highways in Japan are toll roads? They're expensive, too.)

What is this beautiful music? I just need to buy the album!

Oh, you are not kidding. God bless the Mute button.

WARNING: Hit the "Mute" button or turn down/off your speakers before you start playing this video!