I don't think that number in itself matters, other then if the writer wanted to make some point, because the "killer" of the arguement is here:
He cursed them in the name of the lord.
The translation Bohm put is is from the NWT I assume, most don't have the "evil" part in the translation since the word is not there in the original hebrew text ( at least not the ones I have seen).
Cursing in the name of the Lord is taking the Lord's name to do wrong, which is forbidden.
Of course common sense also dictates that God would not be ok with 42 children being killed by bears because they called one of his prophest "Baldy".