Faux leather and textures in and of themselves aren't, but using a faux leather texture on a notebook app to make it look like a real notebook certainly is.
skeuomorph is a physical ornament or design on an object made to resemble another material or technique. Examples include pottery embellished with imitation rivets reminiscent of similar pots made of metal,[1] or a software calendar application which displays the days organised on animated month pages in imitation of a paper desk calendar.[2]
Simulated woodgrain on automobiles is a skeuomorph, such as this station wagon which uses no actual wood construction
Same Wikipedia article: "Functional input controls like knobs, buttons, switches and sliders are often careful duplicates of the ones on the original physical device being emulated."
The save button being a floppy disk (which is no longer used), or a sheet of paper to represent a document (which may or may not ever be printed to an actual sheet of paper) are skeuomorphs by this article's defintion.
Except the save button isn't, itself, a floppy disk, it's just got a floppy disk icon on it. The floppy disk or paper iconography are not "functional input controls" themselves. They are laid upon UI chrome which is likely skeumorphic to some degree, but the icons themselves are not examples of skeuomorphism.
The bookshelves in iOS's iBooks app are. But these could easily be drawn in a Flat UI 'style' and still skeuomoprhic style.
So rich textures != skeuomorphic