You likely used the local IP rather than the external IP. If you google ‘my IP’ on the host machine, it will give you the external IP to connect to – this is different to the local address shown on the server screen.
As mentioned above, you also need to forward your ports. Google ‘port forwarding’ and you’ll find a whole host of websites that can guide you through the process. You need to open and forward port 2010 for Artemis.
If you want to try and set it up ready for next time, just use the forums to ask for help and arrange a session with people to test the connection. There are a few people in the group who could guide you though the process, help test everything and troubleshoot any problems that occur. That way, next time you’ll be able to wow your audience and crack on with showing them how awesome the game is.
One thing re. the tablet. You will have to make sure all clients and the server are running unmodded Artemis 2.1.1 otherwise they will be met with the ‘wrong server version’ error message, or cause the server to crash. This is easily done on a computer – just install the 2.1.1 update over whatever version you are running and it will roll back or update all the relevant files.