Am I a member of the "users" group or not? [duplicate]

Question

Nobody is in the "users" group:

$ getent group users
users:x:100:
$ getent passwd "$USER"
username:x:1000:100::/home/username:/run/current-system/sw/bin/bash
$ groupmems -g users --list
[no output]

Except I totally am:

$ groups
users wheel […]
$ install --group=users --directory test
$ echo $?
0

What's going on here?