Yep. It seems as if it is a BETA track that was in progress, but possibly couldn't be deleted and was left there as a secret, or something. The only way to get the answer is to ask the track creator himself/herself.
It is really odd how'd that be there if it wasn't even intended, but then again there is a canon that brings you there and all, so it seems intended.
If you actually look at the course layout as you approach it, doesn't it look like SNES Rainbow Road? Just saying it REALLY resembles it.
Besides, that's a nice secret the developer put in the buggy track, but don't you think it probably wasted a lot of memory, which could have been used to fix some glitches of the track?
Custom Track: The track inside Underground Sky
Linear Mode
