Why is my ReceivedBufferSize huge? Up to 65535 bytes

Question

So I am playing around with the Tcp protocol in C# and figured I would connect to my server. When I connect to my server it notifies me just fine. but then I go to check the ReceivedBufferSize and it's this receivedBuffer={byte[65536]}

When in reality it only gives back a few bytes.

Why is this happening? Sending this back to my client doesn't do anything either so I removed that part. I figured it's because the packet is so big.

This part right here

byte[] receivedBuffer = new byte[client.ReceiveBufferSize];

returns receivedBuffer={byte[65536]}

public partial class MainWindow : Window
{
    public static IPAddress remoteAddress = IPAddress.Parse("127.0.0.1");
    public TcpListener remoteServer = new TcpListener(remoteAddress, 7777);
    public TcpClient client = default(TcpClient);

    public MainWindow()
    {
        InitializeComponent();
    }

    private void BtnListen_OnClick(object sender, RoutedEventArgs e)
    {
        if (StartServer())
        {
            client = remoteServer.AcceptTcpClient();
            MessageBox.Show("Connected");
            byte[] receivedBuffer = new byte[client.ReceiveBufferSize];

            NetworkStream clientStream = client.GetStream();

            while (client.Connected)
            {
                if (client.Connected)
                {
                    if (client.ReceiveBufferSize > 0)
                    {
                        receivedBuffer = new byte[100];
                        clientStream.Read(receivedBuffer, 0, receivedBuffer.Length);
                    }
                }
            }
        }
    }

    private bool StartServer()
    {
        try
        {
            remoteServer.Start();
            MessageBox.Show("Server Started...");
            return true;
        }
        catch (Exception exception)
        {
            MessageBox.Show(exception.ToString());
            throw;
        }
    }
}

As you can see here, it's only 15 bytes