The article mentions "The OpenFileService part provided a menu option which would dynamically generate a Cyberdog item to a file reference using the Standard Open dialogue [...] to the best of my knowledge is now lost".
A file containing the OpenFileService part does seem to be available here, as part of Cyberdog 2.0 browser install[0][1]:
* https://archive.org/download/cyberdog-evolt_browsers/2.0/Sup...
When it extracted it contains a folder named "OpenFileService 1.0.1 ƒ" which contains `OpenFileService` and a README file.
I found this while investigating some other related items and will attempt to update/edit this comment with some links (but wanted to at least mention this now in case I disappear down some other rabbit hole :) ).
Edits:
[0] Overview page: https://archive.org/details/cyberdog-evolt_browsers
[1] File/directory listing: https://archive.org/download/cyberdog-evolt_browsers/2.0/
Other CyberDog versions on CD found on archive.org (unverified due to online viewer seemingly not able to handle Mac-compatible ISOs) which may also have other relevant content:
* CyberDog v1.1: https://archive.org/details/Macworld_Presents_Top_CD-ROMS_15...
* CyberDog v1.0: https://archive.org/details/cyberdog-integrating-the-interne...
* Unknown version: https://archive.org/details/AppleClubCD2.0.smi
The Internet Archive also has a CyberDog datasheet, "Getting Started" manual and couple of other items.
I found the above items on archive.org after initially looking on https://ftpmirror.your.org/ and http://bitsavers.org which I've had success with in the past when looking for historical info/binaries, especially from archived FTP sites.
While neither site appears to have specific archives of the CyberDog FTP site, I did find a number of OpenDoc & CyberDog related items (including SDK-related) which I'll aim to add links for below.
* CW CyberDog Stubs & Includes: https://ftpmirror.your.org/pub/misc/apple/ftp.apple.com/deve...
* MPW CyberDog Stubs & Includes: https://ftpmirror.your.org/pub/misc/apple/ftp.apple.com/deve...
The above are under the "OpenDoc Development Framework" directory which contains a large amout of other related OpenDoc content which may be of interest: https://ftpmirror.your.org/pub/misc/apple/ftp.apple.com/deve...
There are also CyberDog & OpenDoc assistants & other items here: https://ftpmirror.your.org/pub/misc/apple/ftp.apple.com/deve...
Also:
* CyberDog v1.2.1: http://ftpmirror.your.org/pub/misc/apple/Apple_Software_Upda...
* OpenDoc v1.2.1: https://ftpmirror.your.org/pub/misc/apple/Apple_Software_Upd...
* Misc OpenDoc items #1: https://ftpmirror.your.org/pub/misc/apple/ftp.apple.com/deve...
* Misc OpenDoc items #2: https://ftpmirror.your.org/pub/misc/apple/ftp.apple.com/deve...
And, apparently even the Mac port of "IBM's SOMobjects technology" :D, with which I'll conclude this link dump: https://ftpmirror.your.org/pub/misc/apple/ftp.apple.com/deve... (The relevant binary file is in the parent directory of the `.txt` file.)
Hope the results of my research is of use to you or some future archaeologist!