You gotta be kiddin'! Talk about stubborn. He used a slip stroke several times. On the second shot of the first rack (T=1:34) there is a clear overhead that shows he slips his hand at least 4". There's a clear view of his slip stroke at 3:24 (along with the accompanying sound), and another overhead at 3:41 shows the same thing.
Second rack - at 4:43, 5:52, 6:16, 6:30, and 7:10 all show slips of 1" up to about 4". Below is a composite of three screen captures of the last shot at 7:10. Pretty clear there's a slip of over an 1" since his hand ends up almost off the butt of the cue. You can see he jumped up on the shot, too. lol
The video quality sucks, but the audio is good enough you can easily hear his hand slide along the linen wrap numerous times, even when you can't actually see his back hand. That sound is unmistakable once you've used the stroke yourself a bit (or heard it in the shots where he clearly used it in the video clip). Based on what I can see and hear, Willie not only used a slip stroke, he used it to some degree the majority of the time.
Open your eyes and ears, Lou, your memory is clouding your judgment. If you can't see what everybody else can see, well... we can't see it for you.:shrug:
I think the slip stroke is like the forward press in golf. I was an awful putter prior to incorporating it into my stroke. It's difficult to start a motion without a motion to start it for some players in sports. He definitely used it in these frames. I saw it years ago in pool but rarely and some were like 6-10 inch slips. I don't need it to start my cue forward after drawing it back. But every now and then especially rail shots I have to say to myself any time now. It may be a comfort thing or a way of covering yips.