Quinoa is a pseudo-grain. Unlike true grains, it is not part of the grass family but is made from the seeds of a spinach like plant. It is rich in protein, but like all vegetable proteins, they are not as easy for dogs to digest as those found in meats. Quinoa contains a balanced set of essential amino acids making it a 'complete protein'. It also contains magnesium, fibre, manganese and copper.
Quinoa is becoming increasingly popular in sensitive diets since most dogs have never eaten it which means they have had no opportunity to develop any kind of reaction. The rule is, you can't be allergic to something you have never been exposed to.