The 'Last man' has nothing to do with it. Its not a Law.
It was a reckless challenge, it should have been a straight red wherever it happened on the park.
It was a deffo red in in the box. Looked to me as the 'last' defender was the far side of the action
and the keeper stopped a clear goal scoring opportunity, therefore its a red and a direct FK.
Lucky for the ref, the opportunity to right the wrong presented itself..Happy Days
A reckless challenge only receives a yellow. It has to be excessive force to be a red.