Your version of the question has the qualifier "in local elections".
The parent's version doesn't, so the answer assuming that it talks about the main USA elections, and not local or any random election that just happen to be conducted in the USA, is quite valid.
In other words "in the USA elections" implicitly points to a specific kind of elections (the presidential ones), different to "USA local elections" or "any kind of election within the USA").
You might argue "in the USA elections" doesn't anywhere prevent the more generic interpretation, but I argue that that's how most people would understand and answer such a question.
> Your version of the question has the qualifier "in local elections".
Yes, the point is that qualifier works because when you're talking about people voting "in the USA," you can be talking about local or federal elections. "In federal elections, how many people vote in local elections" makes no sense. "In the USA, how many people vote in local elections" makes sense, because voting in the USA can encompass both local and national elections.
I understand that there are many people who ignore local elections. But I disagree that talking about voting "in the USA" means that local elections should be excluded.
> In other words "in the USA elections" implicitly points
You're using quotations for something that wasn't said. The original comment was "in the USA, can illegal immigrants vote?"
The parent's version doesn't, so the answer assuming that it talks about the main USA elections, and not local or any random election that just happen to be conducted in the USA, is quite valid.
In other words "in the USA elections" implicitly points to a specific kind of elections (the presidential ones), different to "USA local elections" or "any kind of election within the USA").
You might argue "in the USA elections" doesn't anywhere prevent the more generic interpretation, but I argue that that's how most people would understand and answer such a question.