Since Apple launched the Apple iPhone 5s with a 64-bit A7 processor, other chipmakers have thrown their hat in the ring, saying that they too are are working on a 64-bit chip. Even Qualcomm, where an executive had called the 64-bit A7 a "gimmick," has done a 180 degree reversal and announced a low-end 64-bit chip of its own..
Another possibility is that this is related to Samsung's use of Heterogeneous Multi-Processing that can allegedly turn the Samsung Exynos 5 into a true octa-core chip with all 8 cores active at once, like the MediaTek MT6592. Currently, the big.LITTLE architecture on the Exynos 5 allows only one set of four cores to be active at a single time.
The Samsung Exynos will apparently be the subject of an announcement at CES 2014
source: SamsungExynos via SammyHub