class variable VS metaclass's instance variable

foo.rb

class Foo
  @@bar = "123"
  
  def bar
    @@bar
  end
  
  class << self
    def set_bar(bar)
      @bar = bar
    end
  end
end


foo = Foo.new
foo.bar
#=> "123"
Foo.set_bar("456")
#=> "456"
foo.bar
#=> "123"
Foo.instance_variable_get(:@bar)
#=> "456"