I may not be able to answer the direct question of what technologies this specific game uses, but the more general question of what technologies are ideal.
For an MMO-WEB style game Flash (AS3) is an extremely useful client interface for the game. Flash is cross browser and cross platform compatible, and has access to a high level socket layer (used for network communications).
AS3 has two kinds of sockets:
The Socket and the XMLSocket. Now most people make the very faulty assumption that XMLSockets are easier to use, when in reality they are identical except one is meant to parse only XML data (from things like feeds, or web page data), which isn't very useful for games.
The regular plain Socket is what you should spend time learning. Unfortunately there are very few tutorials around the web, as Socket programming is still quite young in Flash, but still very useful.
The basic idea from the Flash (Client) side of things is:
Create Socket Object -> Give It Server IP/Port To Connect To -> Attempt Connection -> Create Listener For Incoming Data -> Wait For All Data On Line -> Use Data -> Send Data -> Listen For Incoming...
Now as for the Server side, DO NOT USE FLASH. Flash may be very useful as a Client, but as a Server it's pretty much useless. You need a language that supports threading, I'm currently using C# as my Server backend so that's the only I can recommend (but it is by no means the only or best option). C# provides easy use of threads and has a similar Socket system.
The Server is FAR more complicated than the Client, as you must manage every connection asynchronously (at the same time), and worry about things like bad data, attacks, disconnects, flooding, overloading, timeouts, lost packets, and a seemingly endless list of trivialities.
You also have to manage all user data, lobby handling, game handling for which I personally use mySQL. It looks super complicated on the surface, but it's pretty much a beefy excel (please no flames for the slack comparison). It's quite easy to make a simple database to store usernames/passwords, or game information, and if you use raw access from C# it's also quite zippy.
So in a nutshell, you don't need a book. Go look for information on simple socket interfaces in AS3 and C# (or a language of your choice, but I recommend C#). Learn about threading and why it's used, there are plenty of great tutorials. Then learn about how games transfer data to and from the server, and why they do the things they do. But before you do all of this make sure you have a STRONG working knowledge of both Flash, AS3 and C#. You should be able to create the game to be made networked in full, start to finish - then only after it is complete add networking last.