"Mirror" is what this question is generally understood to be asking. I don't think swapping the direction of the edges produces a tree in general although it would produce a DAG. I think "invert" could mean "mirror" or turn upside-down depending on the context.
Personally, if I were asked this, I would just say "convert the graph to a matrix, invert the matrix, and then convert the resulting inverted matrix back to a graph", and let them try to figure out if that would work for a bit before joking "oh come on, preorder traversal with a temp var, do you have a more interesting question?"
It would be more leetcode to be given an ordered binary tree and asked to reverse it O(N). It's a lot more fair to the interviewee to be given the explicit task without knowing 'the trick' unless one considers knowing recursive functions to be a trick.
