Great review and he seems very reasonable reviewing it, making educated comparisons to the 1D IV and 5D III.
The AF tracking sounds a lot like 7D/5D III to me. The exact scenario he describes sounds very much like the few AF tracking "misses" I had on the 7D where I'd track something and as long as the colors were reasonably different there was no issues, but on subjects that cross over in colors (football players, birds of a feather, etc) tracking can get easily confused. I've had the same "success" re-tracking a lost subject as well, but perhaps the 1D X is slightly better/quicker-to-focus overall, hard to say without testing it myself.
As for ISO, I agree with "It seems though that the 1D X is comparable to one stop lower ISO on the 5D Mark III". I get the feeling there's every so slightly better dark-area contrast as well although this might be subjective on my part.