No, though it might be ethno-nationalism, depending on their motivations.
I assume this is PvP, where raiding people is what you do - for any reason or for no reason.
There are rules against harrassment though. If they should be punished would depend on what all they said and how they said it, but I don’t think spinning the Wheel of Arbitrary Reasons to Raid and having it land on “they speak Russian” is in itself harassment.