^Dragonspine was new then, plus that sounds like bit of a communication mixup between the writing and visual dept's as Gold's creations though artificial are very much organic and alive that got quickly sorted out. Raiden is nigh certainly intentional given the background lore, no other char coming out around the same time having that quirk (implying it's not a simple oversight) and the visual peeps being by now well used to the peculiarities of that area.
Personal pet theory: Ei's replicants are highly derived and refined Khaenri'ah Ruin Machine tech, possibly with some cues taken from those spoopy Maguu Kenki thingies (which are suggested to be someone's attempts at immortality). The lore only vaguely says she picked up the basic idea from somewhere then spent a lot of time and effort improving it and IIRC Yae at one point offhandedly refers to her having learned the "trick" of transferring souls into inanimate objects from an unspecified "someone" - among the weird in-universe stuff we currently know of those seem to fit the bill the closest.