The
Cud error is caused by a broken die and results in an "unstruck" area on the coin. While your coin looks like a small broken die, the term "
Cud" has usually been limited to coins that have this error on the edge of the die rather than the internal part of the die surface. In recent years, more and more listings have included your type of error.
I personally believe that what you have is actually a Die Chip, caused by a die which is deteriorating and damaged. Someone who tried to create this type of error, by adding a blob of metal, most likely would damage the coin and/or make a dark area on the coin surface where the metal was added.