That depends where the carers were and what they were doing. If they were sitting on a bench 15 metres away from him, then, yes, that’s a problem, but adults with SN can be very impulsive, unpredictable, very fast and very strong.
I worked as a carer for an adult with SN who was 3 to 1 when out in the community, but even then it wouldn’t have been easy to control and subdue them. For this reason, they were usually taken to very quiet areas for walks where they weren’t close to other adults and our route could be varied if necessary. Never in a million years would this person have been taken to an enclosed area like that crocodile enclosure. I doubt they’d have hurt a child but they could easily have become overwhelmed and thus violent through fear and hit out at adults.
The fact this man has been arrested for attempted murder suggests the action was deliberate not a consequence of a meltdown. That is, it implies the child was purposely thrown into the enclosure not knocked in by accident.