How do you make a kills leaderboard include NPC kills?

I have the classic LinkedLeaderboard script, and it doesn't count the number of times I've killed NPCs. I'm not sure why, because the humanoids of the NPCs are named 'Humanoid' just like the player's is.

stands = {}
CTF_mode = false


function onHumanoidDied(humanoid, player)
    local stats = player:findFirstChild("leaderstats")
    if stats ~= nil then
        local deaths = stats:findFirstChild("Wipeouts")
        deaths.Value = deaths.Value + 1

        -- do short dance to try and find the killer

        local killer = getKillerOfHumanoidIfStillInGame(humanoid)

        handleKillCount(humanoid, player)
    end
end

function onPlayerRespawn(property, player)
    -- need to connect to new humanoid

    if property == "Character" and player.Character ~= nil then
        local humanoid = player.Character.Humanoid
            local p = player
            local h = humanoid
            humanoid.Died:connect(function() onHumanoidDied(h, p) end )
    end
end

function getKillerOfHumanoidIfStillInGame(humanoid)

    -- check for kill tag on humanoid - may be more than one - todo: deal with this
    local tag = humanoid:findFirstChild("creator")

    -- find player with name on tag
    if tag ~= nil then

        local killer = tag.Value
        if killer.Parent ~= nil then -- killer still in game
            return killer
        end
    end

    return nil
end

function handleKillCount(humanoid, player)
    local killer = getKillerOfHumanoidIfStillInGame(humanoid)
    if killer ~= nil then
        local stats = killer:findFirstChild("leaderstats")
        if stats ~= nil then
            local kills = stats:findFirstChild("KOs")
            if killer ~= player then
                kills.Value = kills.Value + 1

            else
                kills.Value = kills.Value - 1

            end
        end
    end
end

function findAllFlagStands(root)
    local c = root:children()
    for i=1,#c do
        if (c[i].className == "Model" or c[i].className == "Part") then
            findAllFlagStands(c[i])
        end
        if (c[i].className == "FlagStand") then
            table.insert(stands, c[i])
        end
    end
end

function hookUpListeners()
    for i=1,#stands do
        stands[i].FlagCaptured:connect(onCaptureScored)
    end
end

function onPlayerEntered(newPlayer)

    if CTF_mode == true then

        local stats = Instance.new("IntValue")
        stats.Name = "leaderstats"

        local captures = Instance.new("IntValue")
        captures.Name = "Captures"
        captures.Value = 0


        captures.Parent = stats

        while true do
            if newPlayer.Character ~= nil then break end
            wait(5)
        end

        stats.Parent = newPlayer

    else

        local stats = Instance.new("IntValue")
        stats.Name = "leaderstats"

        local kills = Instance.new("IntValue")
        kills.Name = "KOs"
        kills.Value = 0

        local deaths = Instance.new("IntValue")
        deaths.Name = "Wipeouts"
        deaths.Value = 0

        kills.Parent = stats
        deaths.Parent = stats

        while true do
            if newPlayer.Character ~= nil then break end
            wait(5)
        end

        local humanoid = newPlayer.Character.Humanoid

        humanoid.Died:connect(function() onHumanoidDied(humanoid, newPlayer) end )

        newPlayer.Changed:connect(function(property) onPlayerRespawn(property, newPlayer) end )


        stats.Parent = newPlayer

    end

end


function onCaptureScored(player)

        local ls = player:findFirstChild("leaderstats")
        if ls == nil then return end
        local caps = ls:findFirstChild("Captures")
        if caps == nil then return end
        caps.Value = caps.Value + 1

end


findAllFlagStands(game.Workspace)
hookUpListeners()
if (#stands > 0) then CTF_mode = true end
game.Players.ChildAdded:connect(onPlayerEntered)