Ridiculous. You gave a figure which is not an element of geometry, it's an instance of reality. You attempted to mathematically prove it was something by definition, then applied the operation of negation. That can within geometry, but not in any application of geometry to reality. The figure is a triangle, because of the evidence the figure presents, not because that evidence can be proved.
Wow.
So, in your universe, the figure I posted cannot be proven to be a triangle? Even though it fully meets every definition of the term and is quite clearly to all who see it a triangle, yet this cannot be proven?
If that's the nature of the "logic" in use in science, it's no wonder we're in such a mess.