The claim that elements beyond 94 are only human-made is speculative and probably false. Transuranic elements up to ~100 are believed to be made in, for example, natural fission reactors and extreme stellar conditions. However, it is accurate to say that none of those exist in bulk. They’re more like astatine and francium: so rare that natural occurrence is on the scale of atoms.
Natural fission reactors are pretty slow things, I wouldn't think they would be very good at forming transuranics.
But there's another source out there that we can't see: imagine what's happening in the electron-degenerate portion of a neutron star. The same process that creates the heavy stuff that gets tossed about from mergers is also going to create higher stuff that will decay before we ever see it.
