Não, o acesso não é realmente aleatório, já que as unidades flash USB usam flash NAND, de acordo com a Wikipedia :
With flash memory, only the NOR type is capable of true random access, allowing direct code execution, and is therefore often used instead of ROM; the lower cost NAND type is commonly used for bulk storage in memory cards and solid-state drives.
E :
NAND flash memory forms the core of the removable USB storage devices known as USB flash drives, as well as most memory card formats and solid-state drives available today.