After keeping its shit so airtight this long, I'm 100% certain that it's a deliberate leak.
As big as Souls is among us hardcore, it's not likely to whip up a firestorm of hype among the general population. So a "leak" like this gets the hardcore buzzing and hyped for E3. More importantly, however, it gives this new game the type of attention it wouldn't get when revealed alongside a raft of other, higher-profile megatons.
The screencaps provide a few tantalizing details that make us want to see more, and we'll have to tune in next month at E3 to see it in glorious, living motion.
Sony knows exactly what they're doing. And I doubt Microsoft will be far behind with some well-timed "leaks" either.