This is such a legendary moment. He adjusts to missing a string on the fly with not even a pause and makes the guitar swap super smooth.
SRV was the man.
This is a great example, of if that Gtr tech wasn't watching the exact second SRV turned his head towards him,... he would have missed the signal, maybe fired. He either saw or someone on comm told him it was broke, get a gtr rdy.
We do have body language signals we work out with the artist. "If I turn around to look at you, come swap it". You could see SRV trusted it was coming. Think about this, the pick-up volume knobs on the gtr also had to be set exact as the damaged one. Ya can't blue print this stuff.
What SRV did was some multi-tasking skill. He has to think about how to disconnect strap and cable, hold the cable for the next gtr, sing the verse, and remember where to pick up back in the song. Perfect timing.