I'd say it's 100% the former, as I had completely forgotten that Sekalyns don't bow or even that Aemoten had had such thoughts about the custom. It is a pretty obvious association to make, though... I'd presume such was actually part of its original meaning, along the lines of "my head is yours if I displease you", just as a lot of customs we have today have somewhat outdated and sometimes grim significance. Off the top of my head I can think of shaking hands ("we confirm that our hands are empty and that we are not going to stab each other"), saluting ("I raise the visor of my helmet to let you confirm my identity") and touching glasses when toasting ("we make sure to spill a little of our drinks into everyone else's drinks, so that if we get poisoned, so do they").