All the common domestic ducks in the world are descendants of a single species of wild duck, the mallard (Anas platyrhynchos), except a few ornamental varieties which were domesticated from other species (not at all common). The Indian domestic ducks, which have a history stretching to ancient times in the subcontinent, might also have some genetic component through possible hybridization (done by humans or happened naturally) with another species of wild duck, the gadwall (Anas strepera).

Now, these two wild ducks belong to a subfamily Anatinae (true ducks) in the diverse duck family Anatidae. They are also called "dabbling ducks" as they feed from the surface of the water through a process similar to sieving/filtering, and they don't dive for food. On the other hand, whistling ducks (Dendrocygna spp.) belong to the subfamily Dendrocygninae which is considerably different from the Anatinae and sometimes regarded as a separate family (they are not true ducks). So, there is almost no possibility of hybridization between a domestic duck and a whistling duck (reproductive barrier).

Your duck shows a plumage similar to females of several species of dabbling ducks, including the mallard and the gadwall, which are naturally closely coloured. So, this isn't uncommon. Hope this explanation clears your doubt.

Thanks a lot