Zhang Chi briefly explained why he gave the Dragon Scale to Ao Long first.
Of course, all he said were lies.
He had guessed that Ao Long might be a True Dragon.
The reason was simple; Ao Long and Hong Li acted together and appeared together in the Secret Realm, and Hong Li transformed into a dragon. What about Ao Long?
Both possessed Dragon Blood, and it wouldn't make sense if Ao Long had no chance at all.
This was reason number one.
The second reason was Ao Long's reaction upon hearing She Shishi talking about eating dragons.
Only if she was a dragon herself would the words "eating dragon" enrage her.
Therefore, Zhang Chi directly gave the Dragon Scale to Ao Long.
This was an attempt to curry favor with Ao Long, as well as a test.
If Ao Long didn't accept the Dragon Scale, it would be a good thing, implying that Zhang Chi's guess was correct and he had gained Ao Long's favor.
On the contrary, if Ao Long did accept it, then her heart would be greatly flawed.