>Like making a control call a form method, rather than acting on the data itself, is that considered a "mediator" design pattern too?

Valerie,

No passing the responsibility for something to another object is called delegation. The control delegates to the form.

In mediator we have two (or more ) objects that need to interact with one and other, but we use a third object to hanle the interaction between theo others. The third object is acting as a mediator for the other two (or more) objects.