• kṛta-āsana-parigrahaḥ — having accepted a seat
  Kṛta (made) + āsana (seat) + parigraha (acceptance). The Lord takes the āsana of honor offered. Āsana-protocol is the very issue about to arise — the verse plants the term.
• romaharṣaṇam — Romaharṣaṇa
  Roma (hair) + harṣaṇa (causing to bristle). 'He whose recitations cause hair to stand on end.' A literary-suta name; his speech moved audiences. The defect was not in his art but in his śīla.
• āsīnam — seated
  Past participle of √ās. The participle that becomes the whole problem. Everyone stood; he stayed seated. The grammar mirrors the offense — one verb, but it shouldn't be.
• mahā-ṛṣeḥ śiṣyam — disciple of the great sage (Vyāsa)
  Mahā-ṛṣi here = Vyāsa. Romaharṣaṇa's pedigree is impeccable — he holds Purāṇa-vidyā from Vyāsa himself. Knowledge without humility, the next verses will say, can't override its own absence.
• aikṣata — He noticed
  Imperfect of √īkṣ (to see). A precise, registering verb — not dṛś (general seeing). The Lord registers the breach as data, not yet as anger.

• Whose presence have I failed to acknowledge through laziness?
• What small standing-up could matter more than I think?

The Lord accepts the āsana of honor and looks around — and notices that one man, the very sūta who was to one day speak Purāṇa, has not stood. The defect is small in measure; the position of the man makes it loud. Balarāma's glance is the first reading; the verdict is delayed by one verse.