The problem with this source is that we don’t know if this is a proposal, a prototype modification for study or just a typo error (they do happen even nowadays).
And we do know the Germans tried to upgrade their existing vehicles in multiple ways, leading to new designs due to technical limitations and the Pz.IV series already reached weight limitations with the addition of the long 75mm gun.
Even a quick search on google can highlight all of the issues I mentioned above:
