Sweden has a low population density yes, but that's irrelevant - most is unpopulated land, which doesn't have an effect. If you count Greenland when measuring the population density of Denmark, it's super low, but that would be ridiculous.
More relevant measures would be things like urbanization, where Sweden is number 23 in the world and Croatia number 104 (by https://en.wikipedia.org/wiki/Urbanization_by_country). Or, perhaps, the population density of the most dense areas (5,200/km2 for Stockholm, 4,055/km2 for Zagreb). These are just examples of possible metrics, of course there are many more which might be more relevant, but population density of the entire country has no relevance at all.
More relevant measures would be things like urbanization, where Sweden is number 23 in the world and Croatia number 104 (by https://en.wikipedia.org/wiki/Urbanization_by_country). Or, perhaps, the population density of the most dense areas (5,200/km2 for Stockholm, 4,055/km2 for Zagreb). These are just examples of possible metrics, of course there are many more which might be more relevant, but population density of the entire country has no relevance at all.