As far as I can tell, this was from a British show called "Disco," and it aired in 1971. Great sleuthing on my part -- that's what it says on Youtube.
Anyway, first of all, notice how the women are dancing. A good example is at around 1:22 in. These women look stoned. Or confused. In all fairness to them, it may be because this is not really a good recording to dance to. But this looks like some kind of Brady Bunch slumber party.
Second, Dave himself looks like he's on something.
And what's with the beginning. You see people milling around on the side, waiting for a cue that they can enter the dance floor. And Dave strolls through the crowd, guitar in hand while the guitar part that he is supposedly playing has already started.
But the biggest thing? What's with bowtie guy? There's a guy who's occasionally visible, wearing a yellow shirt, furry vest and a big black bowtie. At 0:29 you can see him in the background doing some exaggerated walk. At 1:17 you can clearly see him playing air tambourine with a huge grin. At about 1:50 he's in the background playing air guitar.
I think the only thing that worked right is that this shows Dave alone -- no band. That, FWIW, is appropriate since he made the recording himself -- producing, engineering, doing all vocals and playing all instruments.
Here's a more recent video: