The Chooser broadcasts a signal to the entire network (or zone, if
applicable) requesting that all devices of DEVICETYPE respond with their
network information. The order in which those devices respond determines
their order in the selection list. (A lightly-loaded network almost always
returns the devices in the same order, because the devices aren't too busy
to respond to the Chooser immediately.)
The order in which zone names are listed depends on the router you're
using. Because this information is usual not dynamically compiled, most
routers sort the list alphabetically for readability.