Isn't this normal? I thought that's how it typically works when an employee leaves a company with any method.
That's what the contract would typically say. But it's not uncommon to have accelerated vesting either when parting on good terms or with severance.
When laying people off, better companies will often accelerate vesting so that the departing employees get additional stock. For example, Google does this:
We’ll also offer a severance package starting at 16 weeks salary plus two weeks for every additional year at Google, and accelerate at least 16 weeks of GSU vesting.
https://blog.google/company-news/inside-google/message-ceo/j...