Why can not I execute other commands while the dialog is running?

The code is from the following video:
http://www.wolfram.com/broadcast/video.php?sx=Ian%20Johnson&v=2076

CreateDialog[
    DynamicModule[{
        vals={}
    },
        Column[{
                Dynamic@ListLinePlot[
                    vals=Reverse@Take[Reverse@vals,UpTo[300]],
Filling-> Axis,
AxesLabel -> {"Time", "Memory (GB)"},
Ticks -> {None, Automatic},
PlotRange -> {0, QuantityMagnitude @ UnitConvert[SystemInformation["Machine","PhysicalTotal"], "Gigabytes"]}
Image size-> Medium
],
Dynamic @ Refresh[
                    AppendTo[vals,SystemInformation["Machine","PhysicalTotal"]-System information["Machine","PhysicalUsed"]]//Latest,
UpdateInterval-> 1.5
]}
Alignment-> Center
]],
VentanaFloating-> True,
WindowClickSelect-> True,
Modal-> false
]

In the video, the speaker executes the previous command and then executes the following:

  • x = rank[500000000]; two;
  • Clear all[x];

To show how the dialog records the available memory changes when storing the expression. But when I execute the command, the new notebook opens (dialog box) but it does not allow me to execute the other command while the dialog box is running.