Yes - anonymous website visits are stored separately from contacts, on an object called a "visitor profile." Eloqua keeps one of these records for each time it gives a visitor a cookie, whether the visitor is known or not.
When a visitor who already has a cookie fills out a form, their visitor record gets automatically linked to their contact record. This means that you can sometimes get information about the activity they performed before they became known.
It is also possible for more than one visitor record to be linked to the same contact record, for example if someone uses multiple browsers or computers, or clears their cookies.