While your assessment may be correct, unless you have known the horse before this trainer got him this attitude is dismissive of the trainer’s skills. It sounds like you haven’t considered that it is the trainer’s work that has brought out the horse’s amateur friendly self. The trainer may now be exaggerating how difficult the horse is or once was (which isn’t really helpful either) so that people realize how much work she’s done.
That need to take credit comes from a place of insecurity, or perhaps offense or irritation that their work is being dismissed because the horse “has just one of those awesome personalities”.
I have a horse with one of those awesome personalities. I got him as foal and did all his training. I have said he’s the perfect horse for me in an “I’m so lucky to have this horse” kind way and someone pointed out that my training had a lot to do with that perfect fit. Awesome personality or not, if they’re not taught the skills of being a good horse partner then they won’t be that amateur friendly, amazing horse that everyone loves.
All anthropodenials aside, he also has a wicked sense of humour (among other emotions).