Not really, but I can see where the confusion lies.
"Random" would assign you a role within a team at random, and your queue time would reflect how long you'd need to wait until the system found you a group with that spot open. Thus, if the system assigned you the role of Mid or Top, your queue-time would reflect how long it would take to get that position if that was what you'd queued for from the very beginning.
"Fill" would search the list of open parties that need a role filled that has not yet been filled and assign you that role. It's still the fastest queue, because you're filling in for the very next available party, regardless of what role they need, but that role is still probably gonna be Support, since people don't like playing Support...