Angia and his companions had come to Sky Palace because they had to. The rest of the Feather race was depending on them to make friends with the Sky.
They wanted to quickly integrate with the population of Sky Palace so they could be considered natural members. When they came there, they brought a lot of treasures to hand out. Blood Feather Knife was one of them.
But it wasn't as simple as handing out gifts to the first Sky they met. They weren't entirely sure how the greedy elders of Sky Palace would react when they made their treasures available. And if the Feathers' goods were simply taken from them, it would do little to grow their relationship with the Sky.
Angia only made the offer to the crowd because Han Sen hadn't come to the knife event. When he put the Blood Feather Knife on display, he had no plan to receive it back.