This is a recent article by Bronkhorst tracing the general picture of the situation of Indian religions at the time of Alexander’s invasion and the subsequent changes that it set off. He argues that an old Vedic society had occupied Northwest India when the Macedonian invasion took place, and it was brutally attacked when the locals rebelled against the invaders. This repression continued under the rule of the Hellenistic states that followed and also by the non-Vedic Maurya Empire. By the time of Asoka, the Northwest was no longer Vedic, the Brahmins having retreated further East. This allowed the greater Gandhara region to become a center of Buddhism under Hellenized rulers, which spawned Sarvastivada and Mahayana philosophy. Etc. The Bibliography is no doubt full of further reading on the subject.
It certainly makes sense to me to think Buddhists originally were not very familiar with Vedic Brahmins but encountered them later in history (though still very early, making it difficult to discern the lines of separation). If Bronkhorst is at all correct, then it would have probably happened when the Vedic Brahmins were forced to move East and South from the Gandharan region after the late 4th c. BCE.
10.1515_9783111427614-010.pdf (154.8 KB)