You've partly answered your own question, probably not realising you did :) The clue is hidden within the field list and the excerpt from /etc/passwd you've provided. See how the fields in the passwd file are separated by a
:? The commas there are a part of the User ID Info field and include the following data: Full Name, Room Number, Work Phone, Home Phone, Other.
If you take a look at the process of adding a user you will see that clearly. Here, see this (taken from a Debian-based system):
root # adduser test
Adding user `test' ...
Adding new group `test' (1003) ...
Adding new user `test' (1002) with group `test' ...
Creating home directory `/home/test' ...
Copying files from `/etc/skel' ...
Enter new UNIX password:
Retype new UNIX password:
passwd: password updated successfully
Changing the user information for test
Enter the new value, or press ENTER for the default
Full Name : Test Name
Room Number : 302
Work Phone : 1234567890
Home Phone : 1234567891
Other : This is just a comment
Is the information correct? [Y/n] y
root # grep test /etc/passwd
test:x:1002:1003:Test Name,302,1234567890,1234567891,This is just a comment:/home/test:/bin/bash
Above you can see where the information was provided by me and where it is stored in /etc/passwd. No stray commas are in evidence.
I can't remember ever seeing a system that had these fields filled-up, however. This additional info is probably left blank by most admins most of the time, except for the Full Name perhaps.