Lets not confuse correlation with causation. All this study shows is people with insulin resistance are at significant risk of dying from Covid, it doesn't identify what actually kills them. However, if you look at the role Vitamin D plays [1] in suppressing cytokine storms, which is what actually pushes over an organism to the point beyond recovery from Covid, and then understand that Vitamin D deficiency is common [2] in Type 2 diabetes, you can begin to understand the fuller picture.

1. https://www.medrxiv.org/content/10.1101/2020.04.08.20058578v... 2. https://pubmed.ncbi.nlm.nih.gov/26375925/