The website went ahead and even photoshopped the front display panel of the iPhone 5s onto the mold itself and found that based on their calculations and estimations, the mold could potentially be used to product iPhones that would sport a display size of 4.7-inches, thus corroborating the rumor.
However the website does point out that the mold is recessed and that they found that if the recessed portion of the mold is to be used, it apparently lines up perfectly with the dimensions of the iPhone 5/5s, so there is a chance that this isn’t the iPhone 6, but one used for the iPhone 5/5s.
They also note that there are holds at the bottom of the mold which apparently could be used to attach something else to it that would allow the wider part of the mold to be used which in turn would have resulted in a 4.7-inch iPhone. It all sounds very speculative so take it with a grain of salt for now, but hopefully additional details will surface at a later date that will either corroborate or debunk the rumors.