One notes that no one, including the authors of this study, is saying that lifestyle and diet are not important factors for the development of atherosclerotic heart disease. What they are saying is that atherosclerosis appears to be associated with aging and that the claims that mimicking paleolithic diets (which, one notes, were definitely not vegan) are overblown. In other words, there is a certain inherent risk of atherosclerosis that is related to aging that is likely not possible to lower further, with the study concluding:
In conclusion, atherosclerosis was common in four preindustrial populations, including a preagricultural hunter-gatherer population, and across a wide span of human history. It remains prevalent in contemporary human beings. The presence of atherosclerosis in premodern human beings suggests that the disease is an inherent component of human ageing and not characteristic of any specific diet or lifestyle.