The alternative offered? To "quit" his job and lose severance and other benefits. Why he (and them) complied? Because he's near retirement age and doing anything else would be end-of-life economic suicide.
That's an involuntary termination, not quitting. When companies try it generally it is a legal quagmire. If it is even slightly questionable companies will generally offer a huge settlement package rather than risk a drawn-out lawsuit fighting in the courts; and since they're leaving the state the drawn-out lawsuit would be in a state they no longer are local to, further increasing cost. I'm curious, did you talk with a lawyer before accepting the deal?
My company has something similar happening right now. Here's where it gets tricksy. At least for employees in CA if they're offered a relocation package as part of the deal and they decline they are considered to have left the company voluntarily. In a way. It does have an impact on their unemployment benefits. So talking to a lawyer is a very good idea when presented with this situation.