4K itself is a silly marketing term. It's not 4000 pixels wide, and conventional resolution naming uses horizontal lines to determine the name. It's 2160p, but that doesn't sound futuristic enough.
This upgraded console is a dumb idea Sony probably mandated to push their 4K TVs.
Consumers have always been sort of immune to the 'numbers got bigger' resolution naming. 720p, 1080p, 2160p, etc. all sound like gibberish to your average TV consumer. The 'HD' branding is what eventually sold 720p/1080p screens. 4k is a term that just sounds better to your average consumer.