I think the sadism fits since it took its time killing both. Its a bit more interesting too.
True sadism requires a psychological association with the target though. The enjoyment in inflicting pain derives from identifying with the other individual to the point that you can put yourself in their shoes and imagine the pain they are feeling. I think it makes the alien less alien if we stray too far down that path. We might view a cat toying with a mouse as sadistic, but that's the result of personifying the animal. I doubt it has that significance for the cat itself. It certainly makes no sense from a survival point of view.
A quick wikipedia look doesn't mention that requirement of identifying with the victim. That's a very interesting concept though. Is that truly how it is?
I think of the alien as being a higher order of intelligence than a cat. That's always been my take. Dolphins are kind of messed up too
The idea of Kane being a closet sadist and the Alien picking that up is a neat concept too. I hadn't ever thought of that angle. Or at least I don't recall doing so. We have to remember comparing the alien to the example of accusing someone of inheriting a parent's negative traits is a different thing entirely. The alien exists (from an in-universe perspective) as something that we don't fully understand. It could merely amplify our normal traits, let alone our abnormal traits.
I just had a look over the wikipedia stuff myself. I think it doesn't mention that aspect because it's written on the presumption that it's being applied to human beings within a society, which is fair enough as there are few animals that are mentally capable of it.
According to that presumption, we naturally project our own state and wellbeing onto the people around us, ideally for the purposes of creating an empathetic bond with those we deal with on a daily basis. True sadism twists that association so that the pain we might observe in others no longer results in pain to us, but delivers pleasure. It still fundamentally relies on putting yourself into the other person's shoes though. A cat toying with a mouse (probably) isn't truly sadistic because the mouse is not an entity it identifies with - it's just potential food.
I'm not seeing anything in Kane that makes me think he might be a closest sadist, but he does exhibit another interesting psychological trait - borderline compulsive risk-taking. At every point in the story where there's a question mark hanging over what to do next, he is the loudest voice spurring them on, despite the risks. It makes his demise poetic, in the same way that most of the deaths in the film are. Brett dies being gormless, Dallas trying to be the fearless captain, Lambert being a nervous wreck, and Parker being all gung-ho. Ripley survives by being "a bitch", as Ridley labelled her during production.