As mentioned above, XCM and Cardistry refer to the same physical activity. But from what I can tell, there are definitely some stylistic differences between XCM and Cardistry in terms of how the community perceives them and what content generally defines the two styles.
The XCM "feel" generally comes across when you see cascades, fans, structure building, armspreads, juggling, springs, drops, catches, card shots and much more sequencing between moves. In my opinion, the reason why these moves give off the more theatrical XCM feel is due to how intuitive they are. These types of moves require very little effort on the part of the observer, as they do not require any prior context to be appreciated in full. For example, suppose we each knew nothing about cards. As a layman, I would most likely find a spring to be infinitely more impressive than a two handed cut. I would have no reason to believe the two handed cut is superior to the spring, the spring requires no explanation as to why it's impressive. But to someone that practices a more empirical style of flourishing, these moves may seem "obvious" or "unimpressive" in design, thus creating an apparent disparity between XCM and Cardistry. Remember, this does not make XCM superior to Cardistry or vice versa. These two styles are still the same manipulation art.
The Cardistry "style" is the opposite end of the spectrum in my opinion, a style popularized by Brian Tudor and the Buck Twins. This idea of intelligent variation and experimentation, where artists focus more on creating complex contextual flourishes designed to impress and inspire other informed artists.Perhaps the best or most observable example of this is the Sybil cut and all of the cuts that stemmed from it. Someone with no knowledge of card flourishing would never be able to immediately discern the difference between Madonna 1 and Madonna 2 for example. But, to a cardist, there are obvious and significant differences between the two. These moves, although esoteric, can be significantly more meaningful to a cardist than older techniques and can result in the creation of even more intelligent concepts. To restate, this does not make either style better than the other. Cardistry can still be intuitive, just like XCM.
A personal example of this in action, I am a huge fan of The Aviv Project on Dan and Dave's website. The moves on that DVD seriously challenged me on a mechanical and a creative level. One of my favorite moves on the DVD is called Broken Triangle, I think it's a brilliant move and the fact that a single mind created this move genuinely amazes me. However, I have NEVER gotten a good reaction from a spectator when performing the move. I would have to slow the move down and perform it repeatedly until the layman was able to somewhat appreciate the idea. As I would find out, most of the moves on the DVD pulled similar reactions. I couldn't even begin to comprehend why such intelligent and creative material only seemed to be relevant to other flourishers. At the same time, I couldn't understand why "cheesy" XCM material resonated with spectators so much more than the other moves I performed. At that point it became evident to me that there was really only one significant difference between XCM and Cardistry.
To summarize, the main difference between the two styles lies in which kind of spectators the performer aims to impress. Both styles are still the same manipulation art at their core and are both equally valid.