If he has a good instructor that should be corrected soon. Kenpo doesn't create a bad temper or arrogant attitude, but sometimes the young ones get a little too full of themselves. That said, some instructors can and do at times contribute to this. But it is never the art, it is always the people. No martial art is about fulfilling an asinine ego.
Sadly, in the right school yes, that can happen especially if the teacher is the shining example and unfortunately there are teachers like that out there who think they are better than everybody else and that they are God's gift to martial arts.
Traditionally no. A good school will take him down a few notches in no time. Arrogance in a traditional school is not tolerated.
Then there are the exceptions like in the one school where this kid and his family pretend that the kids gets deeply depressed if he is not treated better than the other students and told he is better than everybody else.
Martial Arts are being developed with same objectives, to defend oneself or others on any physical threat.
That's why the contribution of certain Instructor is very important, it is his obligation to explain the deep meaning of self respect and discipline and such is the most vital thing that others didn't explain well into their followers.
Some had been arrogant and low tempered, wrong explanation may lead some into wrong path, others showing their extremity to some and such ways ruin certain name, not just an Instructor, or dojo but the style itself.
But sometimes, the practitioner itself trying to track and act on the wrong path, they had been mislead by their personal motives, purposes and objectives; they are a shame on some and discredit the respect which he must gain.
Kempo is one of the styles that is commonly claimed by McDojo and poor teachers with incomplete styles because it's a hybrid style that combines many different concepts from older styles. It's easy to claim hybrid styles as what you teach because you can always argue that your particular style is unique to your own interpretations.
Jeet Kune Do, Kempo, Kun Tao... These are some of the major hybrid styles that are often claimed by those not actually qualified to teach them.
Your friend's shift in attitude is a good sign he's training in a non-legitimate lineage of "Kempo". Any legitimate traditional martial arts teacher (Kempo falls under traditional) seeks to instill discipline and humility in their students as part of their primary and foundation training. To fail to do so is to be a poor teacher.