Last modified: 2014-09-04 07:35:12 UTC
20140728.json.gz is not very explicative, all the other dumps have some sort of prefix. Something like wikidatawiki-, or even wikidatawiki-external- or whatever to give info on format as well, would be best.
This bug is related to Bug 70385, which asks for a more explicative directory structure that follows the conventions used for other dump types.