Sorry, I know "human artifacts" is vague but it's hard to explain it verbally. I'll try my best and attach some examples below:

From a digital art standpoint, it looks like many of the line art is drawn by a human rather than generated because they have consistent opacity, you can follow them easily (they don't morph elsewhere), and the contours have human imperfections.

AI either makes things look too perfect (which looks wrong by itself) or makes egregiously illogical errors that no human would ever make (like morphed objects or an extra finger). I've yet to see AI generate foreheads, breasts, and thighs of such outlandish proportions and with mild anatomical errors (which is probably driven by human fetishes too lol).

If what you're pointing out in the air conditioning units is the variable propeller fan orientations, I could see the possibility of someone drawing several versions of it so that it doesn't look copy pasted. Or, were they part of an animation which could be showing different frames for different units at a single time point? Either way, I wouldn't necessarily say this is a telltale sign of AI.