One and the same, for some.
How was it ridiculous? The "only operating car in the entire city" (an absurdly manufactured nitpick, btw) was stationed at the only operating hospital in the city, which is where Carol was when she got hit (because she and Daryl figured that was where Beth was being held, so they naturally went there to investigate), and the only reason the car was in Carol's immediate vicinity was because they heard semi-automatic gunfire coming from that direction. Carol ran out into the street and thus, was hit by the car that was coming to investigate. They saw that she was carrying the semi-automatic rifle, figured it was she who fired the shots, and then drove off to take her back to the hospital.
They didn't check around for more survivors because A: they probably don't want to add more than one person per group (if they bring in a group of people who all know each other, there's a better chance they'll try to overthrow Dawn's authority/they're less easy to prey on) and/or B: they didn't want to encounter a stronger, possibly dangerous group of survivors.
It's almost as if that was their entire reason for driving around in the car in the first place...
