It is there on Windows 7 and even 10 (just tested it to be sure)! When you drag a window to the side, a sort of circle/drop effect appears around the cursor. I think this is what they are referring to, but I might be mistaken.
That's what's also shown in the screenshot, so I'm pretty sure that's what they're referring to and the feature has always been there, indeed.
It's possible the effect won't show up if you have special effects turned off in the windows performance settings ("adjust the appearance and performance of Windows")