Sugar is a very indirect cause of heart attacks, everyone knows that most heart attacks are a culmination of decades of diet and exercise habits. It's still worth researching everything to do with that, but it's pretty low value research because it's hard to draw any actionable conclusions from it other than "eat healthier and exercise", which is already well known.
The research in the article is talking about a direct cause. Bacteria exists on arterial plaque, viral infection triggers bacteria to multiply, something about that process causes the plaque to detach and cause a heart attack. If that ends up being a rock solid cause and effect, even for a subset of heart attacks, that could lead to things like direct prevention (anti-virals before the heart attack happens) or changes in patient management (everyone with artery disease gets put far away from sick patients) that could directly and immediately save a lot of lives.
The post you replied to was saying that the data from the study isn't as strong as the article and headline make it out to be, which is usually the case. For this one though I'm reading that less as "it's a nothingburger" and more as "it's a small interesting result that needs a lot of follow up".