Does he really say that? If so, he must not have proven any. Few things require more imagination.
Demonstrating a proof can be mechanical, which is why proof assistants such as Coq can work, but finding a proof, that's an art.
http://www-history.mcs.st-and.ac.uk/Biographies/Poincare.htm...
I have to disagree. As theorems become more complicated, proving them becomes anything but mechanical: one must choose between an infinite variety of approaches, many of which are equally valid.