Apparently Lord Sri Krsna was a ksatriya and was not worshipable by the brahmanas. But the brahmanas present there, headed by Srila Vyasadeva, all knew Him to be the Personality of Godhead, and therefore they worshiped Him. The Lord reciprocated the greetings just to honor the social order that a ksatriya is obedient to the orders of the brahmanas. Although Lord Sri Krsna was always offered the respects due the Supreme Lord from all responsible quarters, the Lord never deviated from the customary usages between the four orders of society. The Lord purposely observed all these social customs so that others would follow Him in the future.