Please find the answer to your questions below:
- what this "tree type" command can do, but the other "user type" command cannot do?
In user quota type, the user is target is the user but in qtree quota type; the target is a qtree specified by the path name to the qtree.
-what is "tree_4118314302"? is this an UNIX user id?
This parameter specifies the target to which the quota policy rule applies,For explicit tree quotas rules, this parameter should indicate the qtree name.
tree_4118314302 is the qtree name in the example.
-it is using tree type, but with -qtree "", does that mean this quota is not using qtree?
This parameter specifies the name of the qtree to which the quota rule applies. This parameter is not applicable for tree type rules. For user or group type rules at the volume level, this parameter should contain ""
It should not had have the -qtree "" as it is applicable when using tree quota type. i tested in a lab and when i am going through the command in my ssh session, the "quota policy rule create -vserver <> -volume <> -type tree -target <qtree name> -disk-limit <> " without the need of the -qtree parameter.
https://library.netapp.com/ecmdocs/ECMP1366832/html/volume/quota/policy/rule/create.html