I would assume he used Disk-2-Disk.
Disk-2-Disk: Central Coast, Copier; allows A1020 to read/write C64/128 disks. (From "the Amiga Nostalgia List")
I'd assume you could find disk-2-disk online somewhere. (If not I might have it here and can check for you if you're serious about fidning it.)
[edit] More info:
Disk-2-Disk is an old commercial program for the Amiga by Central Coast Software. There is a demo of it on Aminet (misc/emu/D2D_Demo.lha).
D2D can be used to read data from C64 disks in an unmodified Amiga 5.25" floppy drive. According to the documentation in the demo archive, reading from tracks 1-17 is really slow because the program must do some tricks to account for real 1541 drives having variable speed. (There is a program on Aminet, misc/emu/1541.lha, which can read 1541 disks but this requires that the Amiga drive's speed be reduced physically.)