There's no suggestion that the "Pistons might be after Calderon". It's just someone on a fan site dreaming, like Lakers' fans always dream that they can get pieces they need with their scrubs, that the Raps are eager to help their team out.
IMO, the only way Jose gets traded is if a PG for a legit contender goes down and they're willing to let go of a good young prospect, or promising draft pick, for his rental. Otherwise his expiring is highly unlikely to fetch anything worth the Raptors sending him packing with less chance of re-signing him in the summer at ba reasonable price, which could be important. Unless Lowry picks up his TEAM game in a big way, we need Jose for the development of the young guys.