There is currently no way to distinguish tags/labels from folders in "tag/list" method output.
Sample output:
<object>
<string name="id">user/01234567890123456789/label/bbbb</string>
<string name="sortid">00000020</string>
</object>
<object>
<string name="id">user/01234567890123456789/label/IT</string>
<string name="sortid">00000012</string>
</object>
First object is label, second is folder. There is no way to separate these. One has to make extra call to to "subscription/list" method and process categories from there, then add labels from "tag/list".
Please, add extra attribute to each object of "tag/list" output with name "type", in a similar way as FreshRSS or Inoreader do it, the add attribute "type" with value "folder" for folders and with value "tag" for tags.