the point is that this church wether bogumil or just under manichean influence, was indeed the official bosnian church on wich the king based his legitimacy, all of wich was largely orchestrated by the monarchy itself, as a means of opposing katolic political influence and the rule of hungarian kings
in many ways simillar to the anglican church, as a source of political legitimacy of non katolic sovrein rule, fabricated politicaly using as a base preexistant religious movements directly oposed to papal autority
in the case of the bizantine empire this would mean a usurper emperor who decides to base the legitimacy of his crown on a non orthodox source, obviously not islam, and being politicaly oposed to the katolic western roman empire for some personal or strategic reasons, he therefore alings with some stronger manichean curent preexistant within the orthodox church/es in and around the empire, as both are using this oportunity to seise power it is a natural aliance, and the rate at wich the empire converts to the new faith is a function of the emperors military force and the wilingness of the population to fight for their christian belifes.
probably things would go similarly to the conversion from non christian to christian religion in germanic and slavic populations