Why is the Skype ‘close attachment’ icon when viewing an attachment full screen in the top left?

Is there any reasoning or logic behind putting a 'Close' icon for a native windows application in the top left? (i know mac users tend to go top left to close apps)

I have accidentally closed the new Skype app several times whilst viewing an attachment, just because they still show a "Close" icon for the app in the top right whilst in full-screen mode of viewing an attachment