There's nothing indicating that they hired 11,000 people they didn't need. Many of the people being cut have probably been there for a while but may no longer be needed. The article mentions HR staff being laid off which makes sense since the hiring boom in tech has vanished. I don't think you can draw any conclusions about bad management or mistakes from this, the economy and the tech sector are in a slump with practically every large employer trimming fat. This is just business as usual.