Written Book URL Link Causes OPPED user to op normal user without knowledge

A player asks me to help. I go to spawn and he asks for a book and quill so he can write me what he wants. He then hands me back the book - I open it and it says:
https://www.youtube.com/watch?v\u003ddQw4w9WgXcQ
so I type that in to chrome and get nothing... All the while he is telling me to click it. So when I minimize my browser and see his click it statements I opened the book and click the command.. He was not ready thank god.. It Opped him without my doing... I immediately deop him as he sets himself in creative.