Question: How did the claimers know it was Rick who killed their friend? They never saw him as he ran away while they were inside the house.
Answer: The Claimer in the headscarf saw Rick hiding under the bed just before being rendered unconscious. Also, Rick was wearing a jacket he took from the Claimer he killed.
Chosen answer: They saw Rick run off with Carl and Michonne.
Answer: The walkers could have knocked them down more than once. There may have been another wave that knocked down the fence earlier and they're going to put it up again soon.
Captain Defenestrator