Gness if you had an allergy as severe as the case of this child it would be almost impossible to ever 'eat out' . Eating only your own food would become a necessity just to live safely.
This is the most severe case I have heard of ''reaction even if someone who had eaten nuts spoke to him'' what if someone, staff /guest, had felt hungry and nibbled on a packet of peanuts or a bar of fruit and nut then spoke to him?
The parents are at fault here for allowing the child to get into the situation in the first place . Far safer to take the child's own food than to change the menu for an entire wedding reception .
Another point, the waiting staff were almost certainly temps from an agency , few hotels have sufficient full time staff to do a wedding reception, most agency staff do not have English as their first language and would not be expected to know what satay was or what was in every type of food served.
In my opinion this was a virtual certainty not an accident, the parents did not take sufficient precautions in view of the extreme nature of the allergy.