You're looking in the wrong place. The SSV is mounted at /, not /System. Both /System and /Users are folders that should (AFAIK) exist on the SSV.
You can't do the same test the Reddit poster is talking about while still booted into the SSV/Data volume combo you want to examine. You need to set up dual boot on your Mac, boot the second OS, and mount the original operating system's SSV to see whether it has any user data files on it (it won't).
Alternatively, you can use the command line to see that in principle all your data should only exist on the data volume:
[CODE]% diskutil list
/dev/disk0 (internal, physical):
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *1.0 TB disk0
1: Apple_APFS_ISC Container disk1 524.3 MB disk0s1
2: Apple_APFS Container disk3 994.7 GB disk0s2
3: Apple_APFS_Recovery Container disk2 5.4 GB disk0s3
/dev/disk3 (synthesized):
#: TYPE NAME SIZE IDENTIFIER
0: APFS Container Scheme - +994.7 GB disk3
Physical Store disk0s2
1: APFS Volume Macintosh HD 11.2 GB disk3s1
2: APFS Snapshot com.apple.os.update-... 11.2 GB disk3s1s1
3: APFS Volume Preboot 6.8 GB disk3s2
4: APFS Volume Recovery 1.0 GB disk3s3
5: APFS Volume Macintosh HD - Data 584.1 GB disk3s5
6: APFS Volume VM 20.5 KB disk3s6
[/CODE]
[CODE]% mount
/dev/disk3s1s1 on / (apfs, sealed, local, read-only, journaled)
devfs on /dev (devfs, local, nobrowse)
/dev/disk3s6 on /System/Volumes/VM (apfs, local, noexec, journaled, noatime, nobrowse)
/dev/disk3s2 on /System/Volumes/Preboot (apfs, local, journaled, nobrowse)
/dev/disk3s4 on /System/Volumes/Update (apfs, local, journaled, nobrowse)
/dev/disk1s2 on /System/Volumes/xarts (apfs, local, noexec, journaled, noatime, nobrowse)
/dev/disk1s1 on /System/Volumes/iSCPreboot (apfs, local, journaled, nobrowse)
/dev/disk1s3 on /System/Volumes/Hardware (apfs, local, journaled, nobrowse)
/dev/disk3s5 on /System/Volumes/Data (apfs, local, journaled, nobrowse, protect, root data)
map auto_home on /System/Volumes/Data/home (autofs, automounted, nobrowse)
/dev/disk3s3 on /Volumes/Recovery (apfs, local, journaled, nobrowse)
[/CODE]
disk3s1s1 is my computer's current SSV snapshot. Note that the mount options show it's mounted on /, sealed and read-only. That makes it impossible for any data to be written to the booted SSV.
disk3s5 is my data volume, mounted R/W at /System/Volumes/Data. Through the magic of firmlinks, /System/Volumes/Data/Users is overlaid onto /Users. Howard Oakley has some posts up on eclecticlight.co detailing more about the folder hierarchy of the SSV and Data volume, and how firmlinks stitch them together.
