Don't get confused by the new feature of param hints in RubyMine 2017.1 EAP, from February 9, 2017.
I sure did get confused at first. I was like "what is are those extra characters in my routes file?"
This image clearly shows where that extra
path: is coming from.
It turns out that they are a new feature in RubyMine, to provide parameter help.
I dug into the preferences on how I can customize them:
Enable/Disable the Feature