carpet anemone suggests three seperate species: s. gigantae, s. haddoni, s. mertensii. typically a LFS will bring in some variation of s. haddoni described using the common name "carpet anemone".
a saddle anemone is merely another common name for s. haddoni.
so under most circumstances they are the same anemone. however, due to some identification errors by the wholesalers or fish store, what they have listed simply as "carpet anemone" may infact be the much more challenging s. gigantae, or the hard to find s. mertensii.