It's a complex issue. According to the articles he was officially laid off for "absence prolongée perturbant le bon fonctionnement de l'entreprise", i.e. "prolonged absence that disrupts the operation of the business". That is a valid motive for dismissal, but only where it can be shown that the employee is frequently off sick in a prolonged and irregular fashion, to the point where the company would have to hire a replacement anyway just to keep the business running. It looks as if the company tried it on, and were smacked back by the tribunal.
Strange, though, they they would do this (and have to pay him a separation package that takes into account 4 more years of make-work) instead of just getting rid of him at the start, which would seem to be the cheaper option.
I suspect that, as is often the case in this sort of story, there were personal conflicts and attitudes that we haven't heard about.