A proper CX bike will be designed specificity for CX racing, short headtube, high bb. no guards or bosses to fit them, no bottle cage bosses, cable routing internal or along the top tube, lower geared chainset ie 46/36, sometimes a shaped top tube to aid carrying,
An Adventure bike can have all of the above but usually has bottle, guard & rack bosses, the head tube is probably a bit longer and the geometry a little more relaxed.
IMO you can use a CX as a go anywhere Adventure bike if you set it up correctly but its much more suited to 1hr eyeballs out blasts.
You can use an adventure bike for CX but don't expect it to be an ideal CX bike.