which software are you using catalyst or pixelmad?
the 'power on test' message is just a display of whatever the artnet box cares to send in the message field. it does not mean anything.
artnet and laptop probably dont have compatible network ranges- networks have subnet masks which determine which physical ( or virtual ) interface is mapped where-
this is the sub net mask in the tcpip settings.
artnet is 2.x.x.x
with subnet mask 255.0.0.0
typically on a LAN a dhcp server will generate addresses in the range 192.168.0.x or similar
with a subnet mask of 255.255.255.0
what you probably have to do to enable artnet and laptop network on the same physical port is duplicate settings in network setup -
try google- 'Macintosh multi-homing'
i think - then after duplicating the airport settings - you set the duplicate airport network to use an artnet address.
maybe - this stuff is not very easy to understand.