Do you think that's what the vast majority of people assume when reading the headline?
Context is everything here. If a headline said "Trump discovers through DNA test he's 100% Swedish," we wouldn't assume your definition of "Swedish." We'd assume it meant genetics.
And likewise, if a headline said, "If you're Swedish you're no longer allowed to own a hunting rifle," you would know pretty easily that meant a citizen of the modern country called Sweden. Because it's about law and how it applies.
In the case of this headline, it is ambiguous. It's fair to say people might assume ethnicity. It's valid to point out that it might not be the case.
There's more reason to not actively suppress talk about what "Swedish" means here: When there's a negative story, people want answers and solutions. If a headline is ambiguous about something, and clearing the ambiguity could get us closer to finding a cause, you're doing something good for everyone. If the perpetrators of the alleged crime here were your every-day indigenous ethnic Swede, you'd assume different causes and different solutions than if it were one of a new arrival from a different country, culture, and ethnicity. Maybe some solutions would be the same, but maybe (and likely) not!
What purpose is there of putting forth this one definition of "Swedish" in exclusion to the others, in the context of this headline and the commenter's pointing out of something true? It only serves to suppress thought.
The term "Swedish" as used in this headline likely implies to many more than just this pedantic and America-centric definition of nationality. It's fair to bring up that point.
Developers of simulation games could publically state what biases they put in their ruleset, and even release multiple rulesets with different biases. Maybe a rule-set editor could be included. What would my city look like if people generally put up with taxes? Or if people hated them? Or if education was a quick solution to crime, or a less guaranteed one?