Dunno about that one, but a couple of adopted Russian orphans died from eating the leaves in SoCal a couple of years ago. Seems they were used to foraging for food back in Russia.
The papers at the time said such deaths were rare, because usually the kid will get sick before eating enough for a lethal dose.
I’m not questioning whether oleander is poisonous. I’m questioning whether the scout incident actually occurred or is it urban legend.