No. Because it's a clear motive. It doesn't mean you're a psychopath. It means you are evil. Because you clearly, with all of your faculties in order, chose to carry out a horrible action.
To assume that people with properly functioning faculties would always make moral choices is incorrect.
Don't think you understand what a psychopath/sociopath is. It's not an excuse to do evil things. It is a mental illness technically speaking, but the main problems it causes are lack of empathy and increased boldness/likeliness to act out/act badly. Other than that, they often seem lie totally "normal" people. In fact a lot of sociopaths manage to feign empathy and so can be practically impossible to differ from a normal person. They are fully functioning. They typically aren't suffering from psychosis or lessened intelligence in any way.
Most sociopaths are not killers or even violent. The ones that are do not need motive to hurt or kill. They lack many social skills and do not understand another person has emotions. You are throwing out words you do not know the meaning to. The girls had a clear motive,a sociopath killer needs none.
As i just showed above, I'm pretty aware of what a sociopath is.
I actually said I think one of them is a psychopath, and one is a sociopath, because both of them showed little to no regret, but one of them definitely seemed to be the "leader" so to speak, and decided to go out and kill someone. That type of boldness and uncalled for aggression and want to kill would make me think she is psychopath (obviously combined with the fact she's perfectly calm about the fact she stabbed someone that was supposed to be her friend 19 times). The other girl appeared to essentially just be following what the psychopath was doing, not taking action herself (in other words, not something she would think of just randomly doing herself). That seems like something a sociopath would do. If I remember correctly that's the same girl who said there was a "Bad part that wanted her to do it and a good part that didn't." That slight remorse would also be more indicative of her being a sociopath, since they can start to develop actual feelings of empathy for people very close to them (as this girl was supposed to be).