A xeno is a 'purist' when it comes to animal anatomy. People that don't like to see human breasts on furry characters, or the very human design of the butt (which the gif is of) generally fall into the Xeno category. They are a much more 'advanced' form of furry and not much of the 'mainstream' furry.
Ferals on the other hand are basically full blown normal animals with NO human anatomy what-so-ever except for the eyes, and human-like intelligence. The reason I say that they are one step below Xenos is because while Xeno's tend to be anatomy purists, they still generally accept characters that walk upright like a human.
The primary difference between a Feral and a normal animal is generally the eyes. Humans are the only species in which the sclera (the white part) of the eye is highly visible. Animators and artists use this generally to denote intelligence. If you watch a Disney movie for example that has a wild animal vs. a 'friendly talking animal' companion, the primary difference between the two will be the way the eyes are drawn. The friendly intelligent animal will have visible sclera while the standard wild animal will just have solid black eyes.