The guy wot directed Shadows of the Damned for Grasshoper Manufacture, Guarini is largely responsible for that game's ridiculous craziness, which many people simply assumed was a result of it being "just another Suda51 game!". It's entirely possible Guarini had signed up with Grasshopper for this single production, and his leaving the company is simply an official announcement of the natural termination of that agreement.
Guarini is going to be setting up a new studio, Ovosonico Productions, which seems to be geared around "attitude", or so the website says, possibly involving different forms of media. Sounds like more work than a single studio could handle.