Ancient grain-eaters had clogged arteries too, so meat isn't the cause of heart disease
Nobody serious claims meat is the only cause of atherosclerosis. It has many causes, so finding it in ancient people says little about whether animal foods raise the risk. And the Egyptians who were mummified were mostly wealthy people whose diets were richer in meat and fat than most.
Hardened arteries have been found in Egyptian mummies from a time when people ate mostly grain. That suggests heart disease has deep and varied causes, and it is too simple to pin it on meat. When the evidence is this mixed, diet's role is probably overstated, and we should be cautious about blaming the foods humans have long eaten.
Finding atherosclerosis in people who ate grains does not show that meat plays no part in it. Atherosclerosis has many contributing causes: age, genetics, chronic infection and inflammation, smoke from indoor fires, and diet. A disease with several causes will turn up in populations that lack any one of them. That is consistent with saturated fat and dietary cholesterol raising risk, and the modern evidence that raised LDL cholesterol drives the disease is strong.
The mummy evidence is also weaker than it sounds. Mummification was expensive, so the Egyptian remains studied mostly belong to priests, officials and their families. Temple and tomb records suggest their diets included beef, fowl and animal fat well beyond what ordinary farmers ate. The same studies found hardened arteries in hunter-gatherer and foraging groups too, which points to causes beyond any single food.
The claim also answers a position the other speaker explicitly disowned in the conversation. They said meat is not the only cause. Showing that it isn't the only cause leaves their actual point untouched.
Finally, this is a question about health. Even if animal foods were neutral for the heart, that would not address the reasons most people give for avoiding them, which concern the animals.
Replacing someone's actual position with a weaker, distorted version, then refuting that instead. The original argument is left untouched.
How it applies here: The speaker argues that atherosclerosis is not exclusive to meat-eaters, but the other side had explicitly said they never claimed meat was the only cause. Refuting exclusivity leaves the real claim, that meat raises risk, untouched.