Was this scene in the Ascent of Man scripted or spontaneous?

The Ascent of Man is possibly one of the greatest television documentaries ever made. Jacob Bronowski's expositions on the history of science, knowledge and the human condition are legendary for good reason.

In one of the most profound episodes, where he argues that it is not science that dehumanises people but the false certainties of other people, he visits Auschwitz. He was a refugee from the Nazis and some of his relatives perished in that camp. At the end of episode 11 he claims that, as a survivor and a witness, that he has a duty to point out how many lives were ended there with the ashes of their bodies being flushed into the soil. He says, concluding his argument about science and certainty:

we have to cure ourselves of the itch for absolute knowledge and power

and soon after steps forward into a muddy pool and picks up a handful of mud making a profound point. It doesn't look like the crew expected him to do this or planned for it (he is getting pretty wet and messy).

The scene is moving. But was it scripted or was this something he chose to do spontaneously at that moment?