Yeah, salt's a bad thing, onions are a bad thing, and often even garlic...for dogs. Also, was the chicken cooked or raw? Raw chicken's bad for dogs, though raw beef is ok.
Sometimes if they swallow a huge chunk without chewing properly, they can not swallow it right, so bring it back up. So many times it's not always a big deal if a dog throws up. The best thing is to watch for other symptoms, and if the dog throws up more than once or twice, it might be a sign something's wrong.
If he's acting fine now then it sounds like he purged it himself and will be okay. If you notice him acting lethargic or strange today then certainly get him to a vet.
It was probably too rich with salt or fat (from the sauce) or it's possible (but less likely) that he just can't handle chicken or something it was seasoned with. From now on if you feel the need to share people food with him, be sure it is something bland and unseasoned. He is such a small dog that he could easily get too much salt or something from "people food." Many of the prepared/processed foods we eat, including pot pies and soups, are loaded with salt which can be poisonous in high doses.