It sounds very much like 'journalist-speak'. When they start with "He fell into a canal", they're establishing the boy's innocence - i.e. he wasn't trying to kill himself, wasn't up to anything dodgy, etc. They're also establishing plausible deniability in the event of a libel suit. When they add 'who is said to have jumped off a bridge", they're probably adding conjecture from bystanders, but holding back from saying this as fact, perhaps because of the risk of a libel lawsuit (maybe it's a criminal act due to a byelaw forbidding jumping from that bridge), perhaps because they haven't had enough confirmation to say confidently that he chose to jump - they just know he ended up in the water. So they end up beginning with "He fell into the canal", followed by the reports they've had from one or more witnesses "He is said to have jumped".