This isn't true, it means they had fat to trim. People that were under performing or working on nothing. There was a hiring arms race the last several years and everyone over hired fearing other companies would get talent first. The industry at most of the notable tech companies was bloated.
I don’t know what went on in meta, but a few years ago I worked on a product team in a tech company. That team had a dedicated sub-team who reworked our AWS hosting every year. The company had a full Dev-Ops team to do it for us. Those 4-5 people were just making busy work and design docs in their name. While I’ve since quit and moved on, i hear that team experienced layoffs this spring. That’s “fat” which can be trimmed even if the engineers are very capable people.