I’ve been told that wild birdseed is much higher in fat. It’s marketed toward outdoor birds with an active lifestyle; i.e., they spend enough energy flying around that they need a high-fat diet. Indoor birds who spend much more time just clambering around a cage will not burn off those fat calories and so will develop dietary issues.
Your bird would probably be better off with one of the brands of nutritionally balanced pellets available at most pet stores, or your vet could recommend something probably even healthier (but more expensive).