Why is the roblox engine calling a function in if statement?

So, I am trying to do an anti cheat system and I've tried this script but the problem is that its calling a function in an if statement

local player = game.Players.LocalPlayer
local speed = 10
local mouse = player:GetMouse()
local isFlying = false


function GetMassRecursive(p)
	local mass = 0
	for i,v in pairs(p:GetChildren())do
		if #v:GetChildren() > 0 then
			mass = mass + GetMassRecursive(v)
		end
		if v:IsA("Part") then
			print(v.Name)
			mass = mass + v:GetMass()
		end
	end
	return mass
end


function Flying(p)
	    	speed = 10
			local f = Instance.new("BodyForce")
			f.Name = "Anti-Grav"
			f.Force = Vector3.new(0,196.2,0) * (GetMassRecursive(player.Character))
			f.Parent = player.Character.Torso
			local v = Instance.new("BodyVelocity")
			v.Velocity = (mouse.Hit.p - player.Character.Torso.Position).unit * 10
			v.P = 100
			v.MaxForce = Vector3.new(math.huge,math.huge,math.huge)
			v.Name = "FlyingVelocity"
			v.Parent = player.Character.Torso
			player.Character.Humanoid.PlatformStand = true
			isFlying = true
end


function NotFlying(p)
	speed = 0
	wait()
	player.Character.Torso["Anti-Grav"]:Destroy()
	player.Character.Torso["FlyingVelocity"]:Destroy()
	player.Character.Humanoid.PlatformStand = false
	isFlying = false
end

function KickFly()
	player:Kick("Fly hacking...")
end

while wait(1)do
    if Flying() then
	NotFlying()
	isFlying = true
    end 
end
	if isFlying  == true then
		KickFly()
	end

sorry if the script is too long, but the problem is at line 53