No, they used a tool (SystemTracer) running inside the original Smalltalk that enumerated all the objects in the running image and serialized them in a new image format into a new image file. Every time the image file format changed, it was transformed like this. Smalltalk is very close to a biological system.

That's how I understand what they wrote.

"Produce a new image:

  - Design a new Object Memory and image file format.

  - Alter the ST-80 System Tracer to write an image in the new format.

  - Eliminate uses of Mac Toolbox calls to restore Smalltalk- portability.

  - Write a new file system with a simple, portable interface."

https://dl.acm.org/doi/10.1145/263698.263754

Hmm...I wonder if Dan used the PDF writer I wrote for him to produce that version of the paper...