Resolved questions
「そうだっけ？」について

女性：っていうか、わたしたち、つきあってないし。
男性：えー？そうだっけ？
I'm can't understand what he meant by "そうだっけ？".
I know that っけ is used to make sure of something that was said before, but here it's just used to show surprise? Can I use it instead of そうなんですか？/そうなの？...etc.?

Here's the entire conversation:
http://www.ninjal.ac.jp/archives/Onomatope/manga/assari.html

ありがとうございます。