If we accept AdoredTV as being a Bearer of Truth (*cough...*), the wide span could easily be explained by the usual sloppy/generous comparisons on for instance PR slides of product positioning between generations. Wouldn't read too much into it.
Within the sphere of discrete cards and APUs, if evaluated separately, I can think of various ways to get the sort of scaling done--if you squint at the results at just the right angle. There are potential objections or weaknesses in each, but for example I can see a possible Navi implementation that might be balanced somewhere around Polaris in CUs and other resources, with games being played with GDDR6 speed grades and very low or very high clocks forcing performance into the 580 or Vega 56 ranges for bandwidth or compute performance, with the usual error bars and marketing.
Similarly, there are potential objections to a 20 CU APU, with possible workarounds or compromises.
Combining the two regimes and the order of magnitude spread is awkward in how even the objections do not play well together, and for me enter the realm of needing extraordinary proof or more effort in explanation if they are taken to be close to truth.
I'd like to be pleasantly surprised by some recombination of features, or some new tech that gives a significant architectural improvement.
One irony to the idea of a ~20 CU GPU scaling so far up and down is that if true it would highlight a continued shortcoming of AMD's client CPU graphics options. Intel's managed to have a GPU standard for pretty much forever on its CPU silicon. In this rumor, AMD now has a GPU so effective that it wouldn't need 20 CUs that can match Vega 56 to max out out what the socket's bandwidth can provide. A right-sized GPU with these super-effective resources could be quite small and could make its way everywere, and yet despite the hyped manufacturing revolution there's a rumor with just 2 APU SKUs.
Unless you want to point to it as an indication that the claims are made up, in which case I fully understand you.
That's one of my leading scenarios. I don't have enough information to state outright that it's wrong because of X, Y, or Z. However, even though I cannot definitively state any one objection is irrefutable, it doesn't seem like they can all be explained away with what is given, and many solutions for one will worsen the others.
I'd like to be pleasantly surprised with some new technology or an explanation of new economic or manufacturing trends, however.
The more negative interpretation that might be interesting is that the rumor is substantially true, and the answer to the objection "this might not be true because it may create significant problems along various axes" is "it is true and has problems along these axes". (Also known as the Bulldozer rejoinder.)