People seem to think that because they are capable of one thing it doesn't mean that they are all powerful and everything they have is better then our own.
They might live in a peaceful society where they had no need to make weapons , and the whole idea of killing each other is "alien" to them so it makes seance to checkout our most powerful weapons.
Think about it they can travel between stars in a reasonable time, which means they can fly very very fast.
All they need is an old ship waiting for scrap and tada they've got a weapon that makes nukes looks like firecrackers.