How does Snowball's role in the battle of the cowshed is contradictorily portrayed explain?

He was originally a hero, battling strongly and leading the animals to victory. He took some bullets and was awarded Animal Hero First Class.

However, after being chased away by Napoleon's dogs, he is portrayed as a traitor and he apparently was working for Jones the entire time. Of course, this is just Propaganda, but the animals soon believe him and Squealer.