@VincentYamato yes it is very legal. There is no work law saying what his boss did was not illegal. It's unfortunate to say this but that's how the real world is.
Even if he was a great employee, he was still just a part-timer, companies/businesses tend to lay off part-timers when they are in dire need of an employee reduction, since they haven't been fully integrated into the business.
Due to how unexpected the sales/income of business can be, actions like that tend to happen.
......Well, it should work out for Muu-kun, since he's a real smart fellow. His father-in-law is a professor at a university, so he should be able to help him out