It looks like some of the others have filled you in on the "shiny" nature of your Dratini there. I can promise you you're not the only one with an oddly colored Pokemon like that.

[She tosses out a ball, and her own shiny Golurk pops out and strikes a pose.]

You probably haven't seen a Golurk, or its younger form, a Golett, yet in your journey, but they're usually light blue, rather than grayish black like Robo here.