As a Nano Edition owner I can confirm that I DO NOT HAVE the golden Nanosuit dog tag.
I have however encountered multiple players online who had the dog tag although being under level 20. You get the dog tag when achieving 100 % in multiplayer, meaning completing all assesments. So yes I think the players you met somehow obtained the dog tag by I dunno hacking some data maybe?
I also talked to a 22-Level player who had 'obtained' the dog tag through special 'privileges', he said his brother works at Crytek and that's how he got the dog tag. I could take a picture of that message to prove it.