I noticed that next line of code, the one with ``disabled: true`` has proper " so I thought it was just typo.
Certainly not a typo in the sense of actually typing these characters myself (I've never typed them in my life). But you're right, one of the lines contains proper quotes for Ruby, and the other doesn't. Perhaps it makes a difference whether you type text in the Wordpress editor or paste it from the clipboard? Wordpress' visual vs text editor might also do this different things (the latter also inserts <p> tags that aren't in the HTML code you type). I also found another post with proper quotes, which I assume was pasted rather than typed: