AmritasyaPutra

Can somebody tell me about the difference between the concept of Karma in Buddhism and that of Karma-Yoga in the Gita. I am asking this because, while the Karma concept of Buddhism is in favour of causality, the Karma-Yoga that Lord Krishna preaches in Gita is very deterministic. E.g. Krishna tells Arjuna that you are a mere instrument and destiny has already been decided by me.