That can be taken more ways than you think. They are dealing with it, and that poor child did shoot his mother... but it might still have been a graze.
Except for the fact that Kirkman made it a point to note how well established it is that Carl is a very good shot and would not miss at that close of a range.
Furthermore, given that a knife or a shovel to the head have been shown to cause enough damage to kill a walker, even a graze at that close a range would put one down.
No, given what we've seen in the show, and given what Kirkman said, there is no ambiguity. Any that he's now created would be, as noted before, basically lying.
Lori is still in the credits because she's either in flashback or, like Merle last season, in a dream or hallucination.
They are going to be "dealing with" the concept of a post apocalyptic teenager who's killed at least two parental figures in his life (Lori and Shane), seemed to be considering killing a third (Rick) and what its like to raise that kind of kid in that kind of world. That was already hinted at, both last season and this season when Carl was eagerly about to chow down on a can of dog food. The kid's in real danger of becoming a psycho or feral or both.