Everything is open-source. They block what they want and you can fork it or recompile it. You don't have that same liberty with Google, the Apple Store, Amazon, Samsung, etc.
On the store that you host you can also choose to enforce whichever rules you like.
Plus, they were talking about Gab there. If you think you're going to write the next Gab or... Pander or Flander or whatever that website was that allowed people to plan storming the US capital, then you can still have your own store.
https://f-droid.org/en/2019/07/16/statement.html