What was the code? Are you sure it wasnt an EVAP leak code? These have been semi common on the Emira's.
A decat can't possibly cause a CEL. It is past all sensors in the exhaust stream (by quite a bit of tubing) There is no chance a o2 sensor could pick up on a exhaust leak back at the three bolt mating flange, the slip connection or the muffler. If the leak is prior to the sensors in the exhaust path sure but that would only be if someone had changed out the manifolds/heades. This is likely a case of coincidence with an evap code which has happened more than once now.