Speaking to IGN Italy, the outlet says that the new detail was "confirmed directly by Sony" ahead of the new console's release.
For many, that information might not be hugely relevant - if you're playing on a TV or most gaming monitors, the support for 1080p, 4K, or even 8K is likely to mean you're well catered to. Recently, however, the PC gaming market in particular has seen the introduction of 1440p monitors, so those attempting to hook their new consoles up to their fancy new screens aren't likely to see exactly the effect they might have been hoping for.
If you're confused as to how the console supports 4K but not the smaller resolution, it's worth pointing out that the PS5 will still work with 1440p monitors, but Sony isn't providing specific support for that resolution. That means scaling up or down between different resolutions, which is likely to result in a game that looks a bit blurrier than intended - a shame given the graphical power of the console. Fortunately, however, if you've still got a 1080p screen kicking around (or a 4K one, for that matter), those will work with the PS5 exactly as intended.
It's a potentially frustrating detail to be fully confirmed so close to the PS5 release date, but it's unlikely to have too big an impact on the majority of players, who I'd expect would be playing on their TVs.