Are UML associations unique when there is an association class present?

I'm taking the Stanford edx course (Databases: Modeling and theory) and the lecturer mentioned this piece of information about association classes and what they imply in a diagram (in reference to an example of two classes "student" and "college" associated by a "applies to" association with the association class "appInfo" containing college application info):

Now what we're saying is that association is going to have affiliated with it a date and a decision. What we cannot describe in UML is the possibility of having more than one relationship or association between the same student and the same college.

So when we have an association, that assumes at most one relationship between two objects. So, for example, if we wanted to add the possibility that students could apply to the same college multiple times so maybe, you know, they wanted to apply for different majors, that would actually have to be captured quite differently. We'd have to add a separate class for the application information with separate relationships to the students and colleges.

but I didn't really get what she meant here, does having an association class create an automatic 1-1 coupling between two classes? or is it prohibited for two classes to have more than one relationship? or what exactly is being said here because it's a bit vague and I'm not experienced in UML data modeling.

Solution

The statement is either wrong or it’s taken out of a specific context that was not mentioned here. The reasons are:

there is no implicit one-to-one in an association; the multiplicities at both end of an association specifies if it’s a one to one, a one to many, a many to many association or anything in between.
the same applies to an association class, which is both: an association and a class at the same time.
in a many to many association, there can very well be several times a link between the same objects. In fact, in a one-to-many or many-to-many association, you need to add an explicit constraint if you want to avoid this.

More information:

in this other answer, there are some more explanation about the semantic of association classes
an here a question related to uniqueness. as you will see, it is not that obvious to avoid multiple occurrences