sending post request but returns get request response WebClient c#

Question

Hi I am trying to send post request using WebClient

 using (var wb = new WebClient())
            {
                var data = new NameValueCollection();
                data["TextBox1"] = "myUser";

                var response = wb.UploadValues("http://localhost:16952/Index.aspx", "POST",data );
            }

I am running the ASP.net web forms application on same computer this is load event

 protected void Page_Load(object sender, EventArgs e)
        {
            if(this.IsPostBack)
            {
                int a = 44;
            }

            else
            {
                string b = "avoie";
            }
        }

so when I try to post the else routine executes why? (the name of input is TextBox1)