I think that's a slight misconception. He stated that the top 100 PS4 games
should be playable at launch, but he was also referring to those games utilizing the optimization of the PS5 for improved performance, and that all has to be tested on a case-by-case basis as it's more than just standard backwards compatibility. He talks about it specifically at this timestamp:
It's not entirely clear if this is something just specific to performance improvements with the SSD and optimization, or if this will also impact games running on a normal external HDD that won't be making use of quite as many of the performance improvements, since he did differentiate those scenarios when talking about the SSD and storage.
X![Neo :neo: :neo:](/forums/images/smilies/neo.gif)