Beats me. When I looked up Indigo aka Brainiac 8 while watching the episode, however, her story in the comics seemed to involve the Metal Men, Cyborg, and the Teen Titans...
But I'm guessing there's a more mundane reason than time travel. Speculation: The Coluans were said to be used as supercomputers by the Kryptonians - perhaps Brainiac 8 is a designation related to that.