I didn't see the story mention whether there is a signal triggering movements or these things are preprogrammed for certain movements.
They're heart cells. Pulsing is what they do.
I am deeply creeped out by this, but I'm not sure why.
Are you a fan of Alien(s)? The first thought that popped up when I read Xenobot is Xenomorph.
Perhaps your subconscious is worried about it's potential when it's inevitably weaponized.
I agree. This is one of those things that feels like real science fiction. It feels like the researchers are playing God with parts that they have no idea how they work.
I think I'm in favor of this work, but it is alarming.
Perhaps you subconsciously misread "programmable orgasm".