The comment[0] you reference is more nuanced than your brief copy-and-paste shows, and keeps a more neutral tone than you. Despite that, I'll respond.
Some of the frustration is because millions of people in the U.S. may be losing their service jobs soon and may find themselves in financial difficulty.
Meanwhile many Facebook employees already lead a life of privilege with excellent access to healthcare, free on-site perks, and good base salary and stock options. They are isolated from many of the experiences and problems of the daily grind across the U.S.
This bonus can also be seen as a political move by Facebook to undermine the current administration by essentially 'acting faster' than them in providing a demand-side financial stimulus.
It doesn't seem likely that they've co-ordinated with government or other tech companies on this policy, since not many employers nationwide would be able to provide the same kind of bonus, raising further inequity concerns.
Alternatively it can be seen as a bonus for people who might have been able to cope anyway by adapting their lifestyles temporarily. The median compensation for a Facebook employee is $228,651 according to the article.
Either way it will likely be an interesting decision to reflect on as the situation and political landscape develops.
[0] - https://news.ycombinator.com/item?id=22606846