Hey, husband of that friend here, The bought company had huge debts to the investors (it is a startup, not tiny but small one, ran for several years) and after cashing those out from the purchase deal, the employees were left with shares that were worth 0$. (might be that the founders also grabbed some money out of that purchase, no one knows tho)

The employees of that bought company were given an incentive by the buying company to stay for a while and help tearing down and integrating their product into the buying company.

One could say shady, I'd say that it was just a bad deal.