A few things....
There had been talk of the Marlins dealing Lowell as everyone knows. Less talked about guys that were to be traded were Luis Castillo, Looper, and maybe even Derrek Lee opening up a spot for Adrian Gonzalez to come through. Now that the Marlins have made this commitment to go for this year, they have of course said they aren't trading Lowell. I assume that goes for Looper too, although trading Castillo might still be a good idea.
This trade isn't totally nonsensical. The Marlins need a setup guy because their previous setup guy, Tim Spooneybarger, is on the DL and has been whining about how often he's used. Whether Looper keeps the job all year or UUU takes over, it still makes great real baseball sense as a strong bullpen is a big deal.
Trading Adrian Gonzalez isn't as bad as you may think. They have an even better prospect at first named Jason Stokes who isn't that far off.