My theory is he's just a prick.
Firstly, he may be a prick. I don’t know him.
However, the evidence from those who have played for him wouldn’t support this view. At three clubs he’s built a strong, positive culture by cultivating strong relationships and fostering a sense of collective spirit and responsibility. Lots of evidence to support this.
That said, other factors are at play when assessing the character of a football manager. A key one being whether you like the club he manages. Inevitable hostility will emerge if it’s a rival with added hostility thrown in if he’s successful. Added to this is longevity - dislike grows over time, usually deepening your dislike.
Through this prism of hostility, you’ll then perceive every act with a certain disdain and resentment. It’s quite normal. By contrast, fans of the team he manages will see these same characteristics as being part of his job. Representing the club’s interests with vigorous and front-foot positivity that gives everyone something to rally around. Us against the world, etc.
It’s how tribalism works. But it’s all a bit cartoonish and none of it is a genuine exploration into a person’s character.
The obvious example is Ferguson. Opposition fans disliked his relentless attempts to intimidate opposing managers, his mind games or seemingly influencing officials. A person who many thought to be a hardcore bastard. United fans loved him - obviously.
Yet players ran through walls for him and he clearly had a character and personality that went way beyond the version presented to the media.
In short, it’s all a bit fake and name calling is nothing more than tribal identity.