A dash inside the quotation marks usually indicates that the speaker has been cut off some how or something has occurred that prevents the speaker from finishing his or her sentence. A few examples: someone interrupts verbally, someone interrupts physically (covers the speaker's mouth, physical violence, a kiss), something happens outside of the conversation to distract the speaker (a car accident, some kind of violence or an explosion), etc.


In the case you posted, the dash is being used to indicate an aside. It's the storyteller commenting on the dialogue to inform the reader of something.

So, technically, they're both correct! It just depends on what you're trying to achieve.

Hope that helps!