So no documentary evidence, but you think someone once said it
I don't think someone said it, I watched it being said in one of the 500+ hours of video on the Martin Fleischmann Memorial Project Youtube Channel, and probably the source was mentioned there. The specific comment about the Wardenclyffe was that (even if Tesla did not know why, or suspected why), it produced microscopic iron rich spheres. This, obviously unintended phenomena, was related with the Wardenclyffe being a producer of EVOs, again, wether if Tesla was aware of it or not.