I suspect the "selected by motif" part probably refers in some way to the fact that each etched design (or part of design, such as "two-headed-eagle" etc.) is based on an original of some historical significance or something specific to the original Faberge eggs.
In other words, it's probably a statement that the current work is a copy of some earlier work. I feel that this is backed up by what is stated in some of the websites where the modern glass eggs are available.