I'm not surprised, and it doesn't say anything about Nintendo.
After all, almost all Nintendo fans got the 3DS already, but many Sony fans waited with their purchase of the Vita. Result: as of current, there are simply more potential Vita buyers than potential 3DS buyers. It's not hard to imagine that if that group is set into motion (like the recent pricecut did), the sales can easily jump above the 3DS's.
It's basically like squeezing water out of a sponge. Sony's sponge is still full of water as it has hardly gotten squeezed before, while Nintendo's got some very effective squeezes already. If both suddenly get squeezed equally as much, it's Sony's sponge that loses the most water. But the squeezing is destined to end, and Sony's sponge will continue to hold more water (in this case translated as: will hold a smaller amount of total sales).
Yeah, because a whole weeks worth of sales where a competitor beats you after a bloody price drop by a very small margin truly spells trouble for a company :P
Seriously, I didn't even know that they usually posted weekly system sales or systems that are over a year old. You must have REALLY scraped the bottom of the barrel to find a website that actually gave you this information!
Project Beat a Game a Day, along with my Daily NES Archive: http://www.gamefaqs.com/boards/563947-a-view-to-a-kill