The option will pay Smith more than $10 million and is presently guaranteed for injury, but it does not preclude the Cowboys and Smith working out a multi-year deal before it is fully guaranteed by the first day of the league year in 2015.
Dallas either had to negotiate a new deal or pick the option up by May 3rd, or Smith would have become an unrestricted free agent at the end of 2014. Basically, by guaranteeing Smith $10.039 million in 2015 (the transition tag for a top 10 offensive lineman), the Cowboys have bought an extra year to work out a long term deal. It doesn't lock them into the option until the start of the 2015 league year.
This is a very intelligent move to allow the team extra time to get their cap in order. Smith, the ninth pick overall in the 2011 draft, is already seen as one of the elite tackles in the league. Only 23 years old (he doesn't turn 24 until December), he is pretty much assured of seeing a long term deal worked out at some point. This only leaves Dez Bryant on the team's list of contracts to sort out. A lot of people give Dallas poor grades for this offseason because they only signed four free agents, but the front office continues to do smart, well thought-out things for the long term.