Because Romaharṣaṇa's transcendental realization was not perfect, Lord Balarāma remembered his pratiloma heritage. The idea is that any man may be given the chance to become a brāhmaṇa, but if he improperly uses the position of a brāhmaṇa without actual realization, then his elevation to the brahminical position is not valid.
After seeing the deficiency of realization in Romaharṣaṇa Sūta, Lord Balarāma decided to chastise him for being puffed up. Lord Balarāma therefore said, "This man is liable to be awarded the death punishment because although he has the good qualification of being a disciple of Lord Vyāsadeva, and although he has studied all the Vedic literature from this exalted personality, he was not submissive in the presence of the Supreme Personality of Godhead." As stated in the Bhagavad-gītā, a person who is actually a brāhmaṇa and is very learned must automatically become very gentle also. But although Romaharṣaṇa Sūta was very learned and had been given the chance to become a brāhmaṇa, he had not become gentle.