The key bit comes down to whether the diet-heart hypothesis is correct. Most studies that "show" something to be heart healthy or heart unhealthy are not actually looking at whether there is an increase or decrease in actual heart events from eating any particular thing, they are looking at how it changes cholesterol levels (sometimes LDL, sometimes total cholesterol, depending on when and what we are looking at).
A big reason for this is kinda understandable: to measure the actual heart attack rates and all type mortality over time takes a long time, and particularly with humans that you can't keep in a lab controlled setting for decades (in most countries), there will be a lot of confounding factors. But, if you believe that higher LDL levels causes higher heart attack rates, then you can take a short cut and look at that instead. Indeed, in a mixed diet setup (like the standard American diet, etc) you are pretty likely to see increases in LDL by simply adding saturated fat and not adjusting other things much (probably not guaranteed, and in a keto diet we see it going all kinds of directions). This has been pretty strongly called into question in recent years (actually in research from decades ago as well), with indications in things like the Minnesota Coronary Experiment showing lowering LDL by swapping in polyunsaturated fats in place of saturated fats correlated with a significant increase in death due to heart disease and all type mortality.
The topic is complicated, of course, so there's obviously a lot more to it and some room for debate on either side.