I am on record of having the opinion that there is no real argument against us being a simulation in a general sense, however we frequently find people jumping to quick into the simulation pool and stating there new what-ever-it-is proves the universe is a simulation. The example given above sounds like one of them.
First off, Quantum Error Correcting Code (QECC) are mathematical approaches to allow for stable transfer of quantum information by correcting for decoherence effects. If some version of QECC is apparent in any formulation of quantum mechanics, it is interesting but probably not very meaningful in proving we exists in some sort of emulation. Second, just because it shows up in one theory, unless that particular version is shown to have the ability to predict physical effects then it is hard to make the claim about its relevance.
Whether these things are testable is a matter of debate. However, there are people who are proposing to look for "glitches" in the universe. Some would hypothesize that if we lived in a simulation based on Lattice Quantum Chromodynamics (LQCD) we should be able to find places where the lattice work becomes apparent. This is clearly far-fetched but who am I to judge?
For the World of Warcraft, although I do not play that game, the first evidence of a simulation is along the same lines as the theory to test for LQCD latticework. The pixelation of the characters would be the first indication of potential emulation. The universe as we know it has a continuous spacetime (versus discrete), so any sign of blockiness is a good indicator.
Generally, anything that is an inconsistency with basic laws of physics (e.g. perpetual motion, decreasing entropy, etc) would be the first indicator something was wrong. Now, in WoW one can assume that they might operate under a slightly different set of physics than our real world. So ultimately inconsistencies in some portion of the world relative to the laws of physics would be a flag.
Something you should look into is the Equivalence principle. In a nutshell it is a statement that the laws of physics should be the same regardless of you location in spacetime. It is very critical to our notion of the world around us, but a similar rule should be applicable WoW, and significant inconsistencies would be cause for exploration.