Quick questions: javelins with dueling style and natural weapon proficiency

[Valmark]

Nope. No one has ever quoted any rule to support their claims about game rule constructs.

Feel free to open up the PHB and do so now.

"Returning Weapon
Prerequisites: A simple or martial weapon with the thrown property
This magic weapon grants a +1 bonus to attack and damage rolls made with it, and it returns to the wielder's hand immediately after it is used to make a ranged attack."

From Eberron Rising From The Last War, was quoted twice. It specifically calls somebody that threw a weapon as its wielder. If you go back through the posts you'll find the quote from JNA and Zhorn.