دَخَلَ الْبَاحِثُ وَهُوَ مُطْمَئِنٌّ.
The researcher entered while feeling reassured.
دَخَلَ الْبَاحِثُ. وَهُوَ مُطْمَئِنٌّ بِالنَّتِيجَةِ.
The researcher entered. And he is satisfied with the outcome.
In the first formulation, “wa-huwa muṭmaʾinnun” describes a concurrent state at entry, with both wāw and the pronoun linking it to the preceding action. In a different discourse setting the second formulation can operate as an independent additional report. The mere occurrence of “wa-huwa” cannot settle the analysis.
The decisive issue is whether the speaker is describing the researcher's condition during entry or is making a distinct statement about his opinion. A correct rhetorical classification must follow that intended relation.