<y:State autoResize="false" closed="false" closedHeight="80.0" closedWidth="100.0"/>
in SW-node-fly.graphm (l.73) explicitly turns off resizing (more specifically the autoResize="false" part). If you change that line to
<y:State autoResize="true" closed="false" closedHeight="80.0" closedWidth="100.0"/>
the swimlane node will automatically grow to always encompass its child nodes when these are moved around.
Since it is not possible to create group/swimlane/table/pool nodes that do not automaticaly resize in yEd, there is also no way to turn on that feature in yEd (because we assume that auto-resizing is always on).