I didn't notice that scene being off from what I remember. Maybe it had to do with Rick wanting to not use the gun because it would cause a ruckus, so he had to use the knife....or stick the gun in the walker's head and then fire so it's muffled.
The only part that didn't make sense to me was when dude asked Gabriel to close the gate. Like he literally said, "Hey mind closing that gate? Thanks". It's only the most important duty in your entire life and you just walk away and nonchalantly ask someone else to do it. I guess it goes along with the idea that the Alexandria people are clueless, but I thought that was a bit of a reach. Otherwise, no complaints from me about the episode. So many great moments from start to finish.
I love how it's the gate keeping them alive during the zombie apocalypse and Gabriel shut it as if he was at a barbecue and had his hand full with chicken wings and just shut the sliding door going to the backyard or something.