How does the __call = function work in this Lua OOP tutorial?

Here is the link to the tutorial where I got the following example. Here is the script:

local MyClass = {}
MyClass.__index = MyClass

setmetatable(MyClass, {
  __call = function (cls, ...)
    return cls.new(...)
  end,
})

function MyClass.new(init)
  local self = setmetatable({}, MyClass)
  self.value = init
  return self
end

-- the : syntax here causes a "self" arg to be implicitly added before any other args
function MyClass:set_value(newval)
  self.value = newval
end

function MyClass:get_value()
  return self.value
end

local instance = MyClass(5)
-- do stuff with instance...

I understand the first example in the tutorial to which I provided a link. The main question I have is about line 5 above. How does the __call function work and what is its purpose. I would be really grateful if someone could help me understand this. Thanks!