Here's the relevant bit from that page:
Access to the router through Telnet is prohibited by default. In order to allow this option one needs to use Main_AdmStatus_Content.asp hidden page where s/he needs to execute telnetd command. Actually, the commands can also be executed from the command line, but the thing is that a usual kind of access via telnet is more customary to us.
In order to access the router command line an administrator must specify login and password, which are admin/admin by default. BusyBox 1.17.4 library is installed in Linux 2.6.30.9.
From what I can tell, you can connect to the router via telnet, but it requires a login and password to get in. So you should change the default admin password on the ASUS 330 (like you should do on all routers).
And the article says it is prohibited by default, so there is probably a setting that you have to access to enable it anyway. They aren't very clear about that part.