Share FROM TikTok into my app - React Native

I'm trying to share from TikTok into my react native app using react-native-receive-sharing-intent. This library only gets the url of the TikTok video. I've read through the TikTok video share API, and I do not understand how Instagram and Snapchat is able to get the actual TikTok video downloaded and shared into the app. According to the TikTok for Developers, the sharing only allows into the TikTok, not from TikTok to another app.

Here is an example video that is between TikTok and Instagram.

Do companies like Instagram and Snapchat have some sort of private, corporate relationship where they get private share apis from TikTok and vice versa?

Does anyone know how to accomplish this?

To answer my own question and in line with Martin JK's answer, it would appear that TikTok does have private relationships with the big social media platforms via a supposed TikTok partner program. See response from TikTok for Developers.