Apparently Lord Śrī Kṛṣṇa was a kṣatriya and was not worshipable by the brāhmaṇas. But the brāhmaṇas present there, headed by Śrīla Vyāsadeva, 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 kṣatriya is obedient to the orders of the brāhmaṇas. Although Lord Śrī Kṛṣṇa 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.