PS5 indeed will run PS4 games more than 100 titles up to 4000 title plus enhancemnet with better resolution, or frame rates (possibly better loading time or maybe some graphic visual enhancement)

[HollyGamer]

Sony announces that the "overwhelming majority of the 4,000+ PS4 titles" will be playable on #PS5

PS4 games will run at a boosted frequency meaning possible higher resolutions + frame rates (evaluated on a title-per-title basis)https://t.co/2X6rnXHKnn pic.twitter.com/NOIdSsXJ42

— Nibel (@Nibellion) March 20, 2020

more you can read at https://blog.us.playstation.com/2020/03/18/unveiling-new-details-of-playstation-5-hardware-technical-specs/

and https://www.vgchartz.com/article/442838/sony-overwhelming-majority-of-ps4-games-will-be-playable-on-ps5/

I think indeed when it comes to communication and Marketing Sony is a little bit behind compared to when they announce PS4 back in 2013, probably because they just recently changing their company structure and many policy has change.