Maltose is the product of the reaction. Since enzyme reactions are, in principle, reversible, the product can act as a competitive inhibitor by binding to the active site. Another way to look at it is that the product resembles the substrate and is recognized by the active site. Cyclodextrin is a polymer of glucose with the same alpha-1,4 linkage that is recognized by beta-amylase, and can therefore be recognized by the active site and compete with the substrate.

Are you referring to a feed back mechanism for maltose?

I think it could be described that way: the enzyme activity decreases due to product inhibition as the product accumulates and the need for the enzyme activity is diminished. However, this presumes that the product maltose accumulates in the physiological setting. If maltose, once formed, were consumed by another enzyme or exported, then it would not accumulate and there would be no feedback. For the feedback mechanism to work, it is necessary for the concentration of maltose to be high enough to cause substantial inhibition of beta-amylase.