It appears that Shane has actually lost his marbles. Once the others understand that Randall is gone, Shane stumbles out of the woods and tells the group that he was attacked by Randall, stole his gun and escaped.
Shane then heads off on a “hunt” for Randall with Rick, Glenn and Daryl. Daryl looks somewhat suspicious of Shane’s storyline, but Rick butts in and determines they need to split up to look for their lost prisoner. Glenn and Daryl go one manner while Rick takes off with crazy Shane as Shane planned.