It is possible that AOSP wasn’t removed completely from the board?
It looks like the system was not repartitioned so it is likely there are partitions that are unused. Try running
fdisk on the various /dev/sdX files (sda, sdb, etc). You can also get some clues from the
dmesg logs when the UFS hardware partitions are parsed.
Note that partitioning on UFS is a little complex. There is a hardware partitioning layer (where each partition appears as a /dev/sdX device) and a software partitioning layer (each hardware partition is further subdivided to give device nodes such as /dev/sda1, /dev/sda2, /dev/sdb1, etc).