1997 Subaru Outback

My 1997 Subaru Outback 2.5l engine seized a cam bearing. One cam sprocket broke causing timing belt to come off followed by valve damage, etc, etc. This happened shortly after a repair shop changed the oil and filter. Any ideas about what could have caused this failure?

Age or improper/imcomplete installation of a new timing belt. The shop recent shop visit is unrelated.