The "sickness" was mentioned, I remember. I say sickness with quotes because as far as we(fans) know runners always come up with "exit" strategies where they feel they could lose. Mo knows that the half marathon is Kamworor's greatest strength and though he planned on hunting him down he knew there is a possibility Kamworor would prevail against him and especially that Kamworor had mentioned that he could be going for the world record. To say that he didn't train specifically for it is just as deceptive as the sickness. Mo had hoped for two things in Cardiff: 1. Break his British record and 2. Win the race. Without any chance of either of the two, he would not have wasted his time lining up.
But lets say he was sick. Kamworor beat him that day by 49 seconds. From what I heard before the championships, Kamworor had planned for and was in shape for 58:35 at the worst. That is if the weather conditions were optimum and no accidental fall like it ended up happening. If Mo had been healthy and at his very best, he would not even have come within 20 seconds of Kamworor. That is just to point out that the Kamworor of 2016 is a "wounded" man and in the best shape of his entire career. I know I am a fan of Kamworor and therefore a bit biased but facts are indisputable.