It's one of those moments where, if you stop to think about it, yiu realize that "the thing he did", is not at all trivial.
I feel that way about "golem creation", that doesn't involve spirits possessing dirt.
Making an automaton? Writing an AI? That's fuck-off complicated. Just implementing the sensors is fuck-off difficult.
Indeed. I feel like golems aren't all that well explained in that sense. Though golems are most of the time also really simple, only able to do exceedingly straightforward things. But still those things would demand refined control. If you look at how complicated it has been to make robots that can move like animals or humans, it's been a long, long road and still not yet finished by far.
Like you said, a spirit, elemental, or let's say a reduced soul controlling the golem body would solve all the questions easily enough. I like fantasy where things are explained in some detail, so Xellos here creating a motorbike out of nothing is a bit annoying. Realistically, if a person got all the myriad parts of a bike in boxes, it would still take them a good long while to put it together. Especially so if they hadn't been doing that for a living. But to first make all of those parts is a giant undertaking. By the looks of it, here the "system" aided Xellos 99%, so the bike just sprang into existence.