Very common. Just like on your car. Probably from a stone chip kicked up by another jet on the ground.
However, it’s not tempered glass. That would shatter into millions of shards. It’s a combination of multiple layers of glass, Polyvinyl Butyrate (PVB) and polycarbonate.
The outer layers are usually glass so they don’t scratch as easily. It’s similar to ballistic glass and designed to allow a certain amount of failure (cracks) before it totally fails. I would think that safety protocol calls for immediate replacement upon discovery, even for minor cracks.
But why is one airline repeatedly in the news ? Is it not happening to other airlines.. or is the media choosing to not report on them ?