The drops of Geothermites are not the same as intended.

Geothermites will have a 50% chance to drop a rock if killed during their normal state, while the probability are switched to 100% when shielding. See prefabs/cave_vent_mite.lua:

local function SetUpChanceLoot(inst)
    inst.components.lootdropper.chanceloot = nil

    inst.components.lootdropper:AddChanceLoot("rocks", inst.shielded and 1.0 or 0.5)

    if inst.components.planarentity ~= nil then
        inst.components.lootdropper:AddChanceLoot("horrorfuel", 0.5)
    end
end

However, they will exit the shield state when entering the death state, so the drop chance of rocks will always be 50% upon death.