Should people be able to (down/)vote in communities they dont subscribe?
Yes.
If your admins consider down-voting an act of hostility, maybe they should disable down-voting on the instance. Did they consider the possibility that those accounts they banned were bilingual, and simply prefer to interact in English?
Without the context of the post, the actors, etc. it's hard to justify a position other than, "this is working as intended." Randos bulk downvoted a post, the spike in downvotes prompted mod action. Everyone got to participate and suffer the consequences of their participation.