Oxidizability varies between types of fat. Saturated fat (as the name suggests) doesn’t react as easily. The microbiome (ideally) produces butyrate and other short chained fatty acids, which are required for healthy metabolism. Those also don’t oxidize as easily.
You are the one that's confused if your conclusion is fat = bad for the heart based on this.
Why was this person downvoted? High-fat diets absolutely increase fatty acid oxidation; it's literally one of their (deceptive) selling points.
Why?
That was more a joke. Most health coaches are bad and only read the headlines. That headline could conclude that fat is bad for the heart.
The answere is for sure more complex than easy headlines.