The ability to earn a livelihood is an inalienable right, and I don't understand how it's legally enforceable to have a contractual clause that negates that right.
A clause that one does not reveal confidential information though, is another matter.
If I pay you $325k to sit on your hands for a year and you take a job requiring you to clap all day, you're in breach of contract.. the fact is that the employee is violating the terms of the severance package, not the employment contract. I think there is a meaningful distinction here.
If he didn't agree to the non-compete then he shouldn't have signed the contract.