If the Bhagavad-gita is in the Mahabharata - that's itihasa - how did it get the name Upanisad, Gitopanisad?

Expressions researched:
"If the Bhagavad-gita is in the Mahabharata—that's itihasa—how did it get the name Upanisad, Gitopanisad"

1976 Conversations and Morning Walks

Because it is spoken by Kṛṣṇa.

Morning Walk -- January 6, 1976, Nellore:

Acyutānanda: It already has our name. If the Bhagavad-gītā is in the Mahābhārata—that's itihāsa—how did it get the name Upaniṣad, Gītopaniṣad?

Prabhupāda: Because it is spoken by Kṛṣṇa. Itihāsa also Vedic literature. Pañcama-veda, Mahābhārata, for understanding of the common man. Strī-śūdra-dvija-bandhūnāṁ trayi na śruti-gocarāḥ (SB 1.4.25). Woman, śūdra, and dvija-bandhu, they cannot understand directly the Vedas.