I get it, but they can read it once they're free. Plus, it's super interesting!

Not only is it interesting, and not only is it something they could have left for later

But why would someone be upset at a quick 10 second mental break from work? Take a second to breath. Let out some stress. You didn't send them a novel and require them to read it then and there and throw all of their work off. It was just a quick little micro break.