Question

Which of these explains why the first stage of hinduism was known as brahmanism

Answer 1

The Brahmanism was the the very first phase of what is now known as Hindusim. It was a religion of priests/Brahmans who would perform Vedic sacrifice. So, they were the first Hindu priests to adopt the rituals from the Vedic. The post-Vedic Hinduism accepts the doctrine of Karma. 

Answer 2

The Brahmas were the first Hindu priests who adopted rituals from the Vedic texts and contributed new ideas about spirituality to Hinduism.