What is meant by describing them as "placing their fingers in their ears due to the thunderclaps"?

Imām Ibn al-Jawzī (d. 597 AH / 1201 CE) summarized the scholars' opinions in his book "Zād al-Masīr":

1. They used to run away from hearing the Qurʾān, fearing that it would command them to engage in jihād, out of fear of death. [al-Ḥasan, al-Suddī]
2. It is a metaphor for their turning away from the Qurʾān out of dislike for it. [Muqātil]