How does the site use react and vue at once?

Question

React

Already met many sites with such a joke.
For example, mail ru answers:

On the left, the extension (of the browser itself) says that the page is react, on the right that vue.
Why and how did they do it?

Answer 1

It's very simple - an application on react is mounted in one block, in another - on vue.
Why - the question is not here, ask those who did it.