It doesn't appear to be two partitions, it appears as two separate drives. If it were two partitions on a single drive, you'd see device names like sdc1 and sdc2.
It's likely the drive is implemented as two physical drives at the hardware layer, and depends on a special driver to allow the OS to see it as a single drive. It may also be a chipset limitation (in whatever chipset is used in the thumbdrive hardware).
Either way, it doesn't seem likely that you'll be able to force it to be seen as a single drive. If you require this functionality, return the device for a refund and buy a different device.