Is there a story behind the solo? Was he waiting for a cue or another soloist?
Actually, there are many stories. Some of them are probably true!
My favorite, and the one that seems most likely to me to be true, is that there was an attractive young women who got up and started dancing during Gonsalves's solo, and that caused a commotion, as photographers started to crowd around to try to get a picture, and then other people started dancing in the aisles, and the energy level went up, and the rest is history. Her name was Elaine Anderson, she studied dance and liked jazz, and spontaneously got up and started dancing, first with a partner and then on her own. I've seen how sometimes the actions of one person can transform a crowd, so this story has a ring of truth for me.
There are other stories, such as the one about Jo Jones having been seated just offstage and having sparked the band by smacking a rolled up magazine against his thigh, but I like the story about Elaine Anderson better. What really happened? You probably had to be there.