Any ideas on how this cracked sprocket could happen?

[naetype]

Cleaning the chain last night on the 899 and noticed a bush missing from my chain. New one on me.
Rotated the chain some and then noticed a broken tooth on the rear sprocket. Not THAT unusual.
I went to remove the old sprockets and chain and noticed this crack on the rear sprocket. Another new one on me.

So any ideas as to what is the likely cause of this? Chain and sprockets are AFAM so not particuarly cheap cr@p. Would like to try and avoid this in the future obviously...

[naetype]

No, not owned from new. Found out last Monday it was an ex California Superbike School bike (registered as Ducati UK Silverstone the sneaky sts) then owned by some guy in Falkirk for a year (not MTB). 2014 model, under 15k miles when I bought it, FSH last 2 services including valves done by Ducati Glasgow. So pretty solid on the service front IMO.

[naetype]

New sprocket and chain kit ordered and arriving today hopefully. If the consensus is that it was some impact type of damage that's good, I would be (was) more concerned that it could've been some alignment or fitment issue that I could identify and avoid in the future.