Hello Deborah, and his hair looks slightly damp; that combined with gosh it looks like he forgot to zip his jeans back up. Maybe it was just the laid-back atmosphere or it was hot that night or day.
Or the music was in the key of D; that combined with all the ooh-yeahs could explain the way the atmosphere changed as MSG mentioned. Perhaps it was the orange album cover for the Houses of the Holy disc that stimulated the sacral chakra.
The interior of the Hyatt was decorated in a color scheme of oranges and yellows in 1973, which could explain a lot.