Walton turns 27 later this month and was a third-round pick by Denver in the 2010 draft. He started all 16 games for the Broncos in 2010 and 2011, and four in 2012 before he got hurt. So this is a dude with some real talent and upside if he's healthy. He fits the age profile of the free agents the Giants appear to be trying to sign (a little on the young side of it, actually) and also the overall profile as a guy who hasn't done much in the league yet but has done enough to demonstrate the promise of more.
Should you pencil him in as your starting center in 2014? I doubt it. There remains a chance the Giants could bring back Kevin Boothe at center, and top free agents such as Evan Dietrich-Smith and Brian de la Puente haven't signed anywhere else yet. I can't imagine Walton costs much to sign, so it's likely the Giants are placing a small bet on a high-upside guy who could start for them at center right away if healthy or down the road if he needs some time to get back into the flow.
The totality of what the Giants have done so far in free agency isn't very impressive at this point, but they do seem to have an idea of what they want to do, and their offseason process is a long, long way from complete.