Well this is a little odd, PEGI, the European video game information site, has rated three PlayStation 2 games for release on PlayStation 4. The games are Ape Escape 2, Dark Cloud 2 (Dark Chronicle) and Twisted Metal: Black, all three of which have a release date of today.
The questions are why, and how? Backwards compatibility? HD versions? And why these games? It is, as Toyah would say, a mystery.
Source: PEGI via AGB