What is a 'Wing Loop Fault' on an A320 series Aircraft?
My guess is that there was some circuitry that was playing up. While I'm not sure about 'Wing Loops' specifically, for what I think is a similar example the Airbus A320 series has fire loops in the engines. 

There are two fire loops. If I'm right, it's got little thermal sensors along way, which disrupt the current if they get too hot (or if the wire is broken). Logic gates ensure that both loops must be 'high' for the fire warning to go off. If one is not working, it works from a single input. 

Assuming both of these were working from the beginning, I think it throws a FIRE DET FAULT warning on the pilot information display if one triggers without setting off the other one. I'd imagine that maintenance either disabled the faulty loop within those allowed by the Minimum Equipment List or by changing the part. If it was quick, it was probably the first, but they're not going to go telling passengers that they disabled safety equipment :)