He took an unexposed piece of film from a IP film pack, put it into a 4x5 filmholder (in the dark), exposed it in his view camera, then put it back into an empty film pack (again in the dark), loaded that into his SX-70 - which promptly spat it out (through the rollers) thinking it was the cover sheet to a fresh pack of film. This last step caused it to be developed.
I think.