How big were the angels? How big were the neons? Any fish that's too much bigger than another fish will eat it. That's a well known fact.
The below quote from aquariumfish.net says they aren't compatible tank mates, but it's talking mighty big angels. However, I continue to maintain that angel fish that aren't too much bigger than neons are compatible. By the time my angels are even 6" tall, I won't want them in the same tank with neons anyway.
"As Angel Fish grow larger, they become very efficient at stalking and eating small fish like Guppies and Neon Tetras. So they are not compatible tank mates for these fish."
"Size and Life Span
Angel Fish can grow to be 12" tall and probably taller. I have seen Angel Fish with bodies 6" in diameter, but it is unusual for them to grow this big. Angel Fish are known to have lived for at least 10 years, and with exceptionally good care they can probably live even longer. "