That is not the Steam Box.

Well yes and no, Valve has several partnerships for Steam Box prototypes, but this is one that is actually coming to market. And Valve does have an active investment with Xi3's Piston, which has been touted as the "Steam Box" since CES. I wonder what happend to the 1TB storage option and why they decided to go solid state only though, which raises costs.

Is Xi3's Piston the Steam Box?

Sort of. It is not made by Valve, though it is associated with Valve. Some companies, like Xi3 with Piston and NVIDIA with Project Shield, are working with Valve in some capacity. In some cases, like with Xi3, Valve has even directly invested in other companies. This is likely to help the companies produce hardware that might be appealing to a more general audience and then only talk about Steam games, as opposed to PC games. Valve has said we should expect more announcements from other companies about different styles of gaming machines throughout 2013, but those won't necessarily be the official, Valve-produced Steam Box.

Just to be clear.

It is... in your link.

However, Newell has since confirmed to The Verge that while the Piston will be a notable Steam Box, it will not be 'the' Steam Box, which Valve will reportedly produce itself.

In fact it is a Steam Box but not the Steam Box sold by Valve... others companies can make you own Steam Box via partnership with better specs maintaining the same desing. 

misleading title :(

Why?

This is probably the idea, because it really isn't too much different from hooking a PC with Steam up to the TV and hitting the Big Picture option, which I already do. It's still kind of buggy though.

Maybe I should edit the title to make it a bit more clear.

It is "a" Steam Box, as in a box that is "Steam enabled." It is not "the" Steam Box, as in Valve's "console killer." To say otherwise is misleading, not unlike calling Asus's Vivotab the Surface.

I edited the title to make it a little less misleading. Sounded like it was the only Steam Box.

... the steambox isn't revealed until Valve reveals it - maybe it is the same thing in the end, but this whole "Valve is invested in that company so this must be the official steam box" crap is starting to get annoying, wait for the real announcement