In his tafsīr of the verse you are asking about:
بَدِيعُ السَّمَاوَاتِ وَالْأَرْضِ ۖ أَنَّىٰ يَكُونُ لَهُ وَلَدٌ وَلَمْ تَكُن لَّهُ صَاحِبَةٌ ۖ وَخَلَقَ كُلَّ شَيْءٍ ۖ وَهُوَ بِكُلِّ شَيْءٍ عَلِيمٌ
[He is] Originator of the heavens and the earth. How could He have a son when He does not have a companion and He created all things? And He is, of all things, Knowing.
— Surat Al-An'am 6:101
Ibn Kathīr quoted Al-'Awfy saying that:
وَخَرَقُوا لَهُ بَنِينَ وَبَنَاتٍ بِغَيْرِ عِلْمٍ
For they have attributed to Him sons and daughters without knowledge.
— Surat Al-An'am 6:100
This is not talking about any specific group as such. There are several groups that had a notion of Allah having sons, daughters, or both, e.g., Egyptian Horus, Indian Krishna, Indian Mitra, Persian Mithra, Mexican Quetzalcoatl, Syrian Tammuz, etc. All such groups have similar notions of a savior son of God.
The word walad in Arabic is better translated as offspring as it has the same root origin as to give birth. This is a form of ridicule by irony. Ibn Kathīr explains that to have an offspring, it means there would be an equal to Allah, let that be the offspring, or a wife through which the offspring is obtained, or any other of His creations, and Allah has no equal and no match. The irony is: If Allah does not need a consort to have a son, why would He need a son in the first place as a sacrifice as is the case in the stories above? Needless to say, this is not limited only to Horus, Krishna, etc., but to any other similar notion.