انظُرْ كَيْفَ يَفْتَرُونَ عَلَى اللَّهِ الْكَذِبَ ۖ وَكَفَىٰ بِهِ إِثْمًا مُّبِينًا
“See how they fabricate lies against Allah — this alone is a blatant sin.”
This is the specific asbab al-nuzul: classical tafsir (e.g. Ibn Kathir) records Ka'b ibn al-Ashraf's words to the Quraysh -- quoted in the post -- as the occasion for this ayah's revelation, condemning those who call disbelievers "more rightly guided" than the believers.