It is perfectly normal for this to happen. When you connect to a terminal remotely, bash performs a reverse DNS lookup. This will only be the case if the host name is not specified on the network from which you are connecting and there is no response from the DHCP server or if reverse lookup at the remote DNS server fails.
You can easily override the default setting by using this command in Terminal:
# sudo scutil --set HostName archos
You can check it by using:
# nslookup nn.nn.nn.nn ( or ) # host nn.nn.nn.nn
(where nn means the IP address of your Mac)