وَأَمَّا ثَمُودُ فَهَدَيْنَاهُمْ
As for Thamūd, We guided them.
The structure after أَمَّا involves segmentation, its response and pronoun links. The naming of Thamūd and the pronoun in هَدَيْنَاهُمْ must be analyzed in their own syntactic positions.
A construction with ammā should not be forced into the same analysis as a bare “Zaydan ʿaraftu.” The discourse particle changes how the sentence organizes its topic and predication.