Is this lesson outdated in 2019? I can follow this mostly, but opening the sprites is difficult for me. As I open it exactly as you say, I can't get them to open. Is there a reason? Maybe this lesson's a bit out dated and either the files are old or there's an updated way to do this?
I downloaded them and was able to import them into the latest version of Unity. What issues are you having specifically? Just to be clear, you'll need to unzip the project files and within the project source files folder you'll find individual Unity packages. You can double click them to import into an existing project. It's best to have an open project ready to go. Sometimes if you just double click them without Unity open it'll hang up and/or not work as intended.