Unexpected data passed as a first function argument

[_provector]

I have a function call like this:

local movementVector = Vec3(-axis.x,0,axis.y)
local camRotation = self.camera:GetRotation(true) *Vec3(0,1,0)
local rotationAngle = tonumber(math.floor(camRotation.y));
local rotatedVector = self:RotateVector(movementVector,rotationAngle)

And a function definition like this:

function Script.RotateVector(unexpectedStuff,vector3,degree)
	--For some unknown to the universe reason a table type is being passed here as a first argument	
	local cosinus = Math:Cos(degree);
	local sinus = Math:Sin(degree);
	local newX = vector3.x * cosinus - vector3.z * sinus;
	local newZ = vector3.x * sinus + vector3.z * cosinus;
	return Vec3(newX,0,newZ)	
end

It took me a bit of debugging to see why my Math:Cos function was getting Vec3 instead of a plain number. In the scenario above I had to put extra argument in function definition called "unexpectedStuff" as I noticed a table type is being passed to the function upon call. I have no idea why, first time I see something like that in my experience.

Attached is a full player script I encounter the issue in. 

Test.lua