"We narrate to you their story in truth" means: their news. "And We increased them in guidance" means: in faith.
﴿نَحْنُ نَقُصُّ عَلَيْكَ نَبَأَهُمْ بِالْحَقِّ﴾ أَي: خبرهم. ﴿وزدناهم هدى﴾ يَعْنِي: إِيمَانًا.
