Ooooohhh-- the video explains it! Thanks for the link! Right-- okay, try doing this, instead: Pick up a stitch-- you can do one, or several in a row-- coming the other way, with a needle in your left hand. Then with the 2nd needle in your right hand, purl off of it, as if the stitch (or stitches) on the left needle were live instead of just picked up, if you know what I mean. It isn't the way you're used to doing it, but it will get you what you want, and you might be able to figure out how to do it the video way in purl, after you've done that.
To do it the video way, but in purl: do you see at about the 58 second mark, she's pushing the needle into the stitch she wants to pick up, away from her. Then at the 1 minute/1 second mark, she's taking the needle and going over the working strand of yarn then behind it, and then catching it and pulling it through the picked-up stitch, towards her? To do it in purl, do this:
Come from behind the stitch you want to pick up, with the needle and poke it through towards you. Then come above the working strand of yarn, then in front of it, and then catch it and pull it back through the picked-up stitch, away from you.
Try both ways and see which you like better.