nope this is entirely legit. Valve confirmed that when they shipped the 300 steam boxes today to beta testers they'd also push live Steam OS Beta. Check the github and steamstatic.com files.
This doesn't mean that downloads from steamdb.info or steamstatic.com are legit. Tread carefully, I'll wait until there's a link from an official site.
steamstatic.com is where the deb packages for the Steam Linux client are hosted.
steamstatic.com is a valve domain, look at its nameservers whois.net/whois/steamstatic.com