Does the concealment from Aisha (may Allah be pleased with her) of Aaron's sister not indicate her knowledge, or is the mentioned narration not authentic?

Al-Tabari reported a narration from Muhammad ibn Sirin that Ka'b said to Aisha, may Allah be pleased with her, regarding the verse: (O sister of Aaron), that Aaron was not the brother of Moses, peace be upon him. Aisha disbelieved him, so Ka'b said: If the Prophet, peace and blessings be upon him, said it, then he knows best, otherwise, I find six hundred years between them. Aisha then fell silent.

The chain of narration for this report contains an ambiguity (I was informed that Ka'b), and a narration with an unknown narrator is not accepted due to the lack of knowledge about their uprightness and precision.

Assuming the acceptance of the report, Aisha, may Allah be pleased with her, did not intend that Maryam was a literal sister to the Prophet Aaron, but rather intended a siblinghood of lineage, meaning that her ancestry traces back to the same branch from which Aaron came, as was the custom of the Arabs in attributing a person to their tribe with the term "brotherhood" (e.g., brother of Banu such-and-such).