Which inference from the past verb jāʾa within idhā is unjustified?

Supplementary Practice 22: Comparative Rhetorical Study of Sūrat al-Kāfirūn and al-Naṣr

• Identifying it as morphologically past
• Inferring an exact historical date solely from the past form
• Seeing it as part of the circumstance framed by idhā
• Connecting the clause to the subsequent response