No, not autoimmune. It's basically kidney stones in your joints. It is caused by high levels of uric acid in the blood (hyperuricemia). The uric acid forms crystals in the joints, shredding tissue and cartilage, causing pain and inflammation.
It's generally agreed that while diet has an influence, it's not the only factor. Some are predisposed to developing gout while others with the same diet never do. Reduced kidney function, excess alcohol consumption, obesity, medications, and a bunch of other stuff can all contribute.
For severe acute flare-ups Prednisone is very effective at reducing inflammation and pain. If the gout persists, there are medicines that can decrease uric acid concentration in the blood.
I spent an embarrassing amount of time trying to figure out who Dr. Congo in Rwanda is