Chinchilla wagging his tail!

Hi, hello! New to this forum site. :> Not entirely new owning a chinchilla, just never seen this behavior from them before. I only have the one, his name is Pippin. We call him Pip! I got him from a pet store, I know, shame on me! But they said that he had been in there for about 2 months and everyone kept adopting out the babies and it broke my heart. Anyways! I believe he is 6 months old or around that age, he's not very big and looks like he has a lot of growing to do! I've had Pip for 2 weeks now, and he seems to be very content. We're learning his schedule of when he wants to play and letting him come to us. Well, around 7:30 this morning, he was awake and sitting by his cage door. We usually take that as, "Hey open this door! I want out to play!" Well, I decided to open the door, and he did his usual sniff my hand, run around, jump on my shoulder and back into the cage. Then he was letting me pet him. Then he started wagging his tail from side to side and making little squeaks! And a few hours before this, he decided to "charge" at my hand. As though he was playing and with the same squeaks. At first, I thought he was annoyed, but when he's annoyed or had enough, he just runs to the lower level of his cage.

Everywhere I have looked, it said that they do this when they want to mate. But other posts about it have been about two or more chins involved. Pip is the only one I have. He's not vocal either, he's very quiet. Very sweet boy too. So really, I'm just wondering why he would wag his tail and make squeaks at me for petting him. Surely he doesn't think I'm another chinchilla? Was he asserting dominance? He has never bitten any of us, does his little nibbles, but has never seemed angry. Any insight would be great! :)