A summary I read on TV Tropes or something reminds me that Jack does feel bad about killing robots if they're not evil, but apparently the emotional connection is different when it's a human.

Thanks for pointing that out to me. I found the quote:

There were multiple occasions where Jack was fighting something that seemed organic only for him to cut into it & it turns out to be a robot. I say "robot" as opposed to "cyborg" as Season 5 is strongly suggesting that he never killed anything that wasn't a demon or a mindless monster or something.

I honestly don't remember this episode, but since the series had a tendency toward things turning out to be robots even if it made no sense, I probably just assumed they were robots.

"This season will explore Jack killing a human for the first time."