I'm not sure I understand exactly what you are trying to get but I will try to help.
Matlab nomenclature usually refers to the window as a "figure" while the graph is the boxed area that the data is displayed. You can have one figure window with multiple graphs (or plots or axes) on it. With 30 different graphs the window would get pretty crowded though.
If you want one figure with set of axes and all the data on that same axes you can use
hold on
command and the data won't erase when you plot something else. Make sure to use
hold off
after the loop to disable the behavior.
This is used some on lines 45 and 54. Also the first figure is created using
fig = figure
and is recreated and overwritten each time in the loop. If you want all the data in the same figure you can create the figure once before the loop starts and use the value in the variable fig as a handle reference.
Also on line 44 the figure is again calling the fig handle to plot.
Somethings to look at that may be useful are subplots and handles.
Let me know if this helps and if you have any further questions.
EDIT:
Try this as an example to understand the plotting behavior.
dat = rand([10 20]);
figure(); hold on
for i = 1:20
plot(dat(:, i));
end
hold off
