Enhanced CDs (Audios CDs with some extra ROM content) are multisession. They will have an audio session followed by the ROM session. These 2 sessions each have their own leadin and leadout.

If you look at the very inner part of your picture (just after the part that looks black with numbers in it) you will see the first session leadin. At the very outer edge you will see the second session leadout. The small band you are asking about has the same appearance. I believe what you are seeing is the 90 seconds of leadout and the 60 seconds of leadin that must be between sessions. This 2.5 minutes would take up about 1mm of space at radius 52mm to 53mm.

The majority of the data in leadin and leadout is nothing but zeroes. It is normal for these encoded areas to have a different appearance than actual audio tracks and ROM tracks.

RM