PvZ XBLA "will deliver more game content than any previous iteration of the franchise, boasting seven game modes, including two all-new multiplayer modes, 12 unique achievements and 21 mini-games," says PopCap, and cost 1,200 MS Points ($15).
The supposed listing mentions "VS. mode" and "Co-Op Wall-Nut Bowling," which would most probably be yet more "mini-games" separate from the main campaign mode.
The achievement listing will almost certainly have come from Microsoft's Partnernet, though developer PopCap has yet to announce any multiplayer modes for PvZ on XBLA or even a release date, despite confirming the release way back in July 2009.
PopCap has asked us "save the date" of August 2 for something Plants vs. Zombies-related. The company explained at the Develop 2010 conference last week that it was hoping to integrate more social features into its future games.