If you had ethics divergence, it might have been possible to engineer a situation where you had Spiritualist pops with a climate preference for the vassal's worlds, and that tragically were unemployed* and lacked housing**, at which point this lump of excess population was expelled*** and ended up seeking refuge on those robot worlds. With no other sentient pops, a single Spiritualist pop should make the Traditionalist faction reach 100 % support**** and make the AI inclined to change ethics.
* Since Workers are usually less happy, and unhappy pops are more divergent, chances are that the Spiritualists would pop up in the Worker stratum. Especially if there were unemployed pops. Otherwise, the corresponding Worker job could just have the slots reduced until the Spiritualist pop goes unemployed.
** By disabling or destroying buildings/districts that increase locally available Housing.
*** I am actually not sure how the game determines which pops are considered "excess population". In my opinion it should be unemployed pops, but I can't rule out the possibility that it is just a random pick. In the latter case, this technique might be too unpredictable unless you relocate non-Spiritualist pops to other worlds before the expulsion. (Does anyone know how the excess expulsion mechanics actually work?)
**** A minimum number of supporters may be needed for a faction to appear.
