The answer to your question would be that a dash is appropriate in the sentence above to set off a parenthetical expression.
A parenthetical expression is a word or words added to a sentence without changing the meaning or grammar of the original sentence. They give extra information that is not essential. Therefore, parenthetical expressions can be removed without altering the sentence's meaning. When nonessential information is added parenthetically to a sentence, it is separated from the main sentence by commas or other punctuation. In this case, the parenthetical information is separated by means of the dash.
