The instructions for the Lonely Cowboy are frustratingly vague. It says he "replaces the robber", but it isn't entirely clear whether that means he still functions as the robber (in addition to the new Cowboy rules) or not.
I'm guessing the Cowboy still steals cards, as that's the only way I can figure to interpret the "singing for supper":
When the lonely cowboy visits you, he will sing for his supper and you will gladly pay him.
Whenever you roll a "7", the usual actions are carried out normally. (Discards (if any), move the cowboy, "sing" for a card etc.)
However, once again, this is not made explicit.
The next question, then, is does he also block hex production just like the robber?