No Mr. Kuddo it's the other way around and your facts wrong (although they were probably correct at the time). USB flash drives can store up to 256gb now, although you probably meant 16gb, not 18gb. They access very quickly because there are no moving parts.
USB HDDs (hard disk drives) can store in excess of two terabytes of data. That's an incredible amount of photos, videos, music or whatever you want to store. However read and write access times of a HDD to a flash drive are vastly different.
HDDs have to spin up, usually at 5400 RPM and wait for the head to find the right place on the platter, where it then reads it off the disk in a linear order, whereas flash drives have no moving parts and can access data instantaneously.