That is known as "wall surfing" and is the most entertaining thing to watch a chinchilla do. To me anyway.
Most chins don't like to be petted but it is something they can be acclimated to once they get to know you and often become more cuddly when they get older and slower. My first chinchilla, like most, really liked being scratched under the chin as soon I got him to tolerate being touched but rarely liked to be held. He liked it so much that he would close his eyes and fall over backwards because he'd lift his front leg up and lean back too far.
My second chin is very tolerant of being held but rarely accepts being touched along the jaw or neck to get a chin scratch. He is generally intolerant of being scratched and stroked for anything but a short while but sometimes if I pet his head right he'll fall asleep in my hand. So ya never know what you're gonna get.
