You kinda have to take what they say officially with a grain of salt, since they too can use any kind of scapegoat to gloss over the problem. And they do have a very clear incentive to drive away bad perceptions of the layering technology, since they’re likely to use it for the next expansion (no source, just makes sense since sharding is already overloaded with negative PR).
As for exploit or not, they gained a competitive advantage through a glitch. Literally the definition of it in their own ToS. The GM is at fault for approving it.
Keep in mind, Blizzard hasn’t upheld rules for a very long time. They’ve followed the marketing approach to make it seem like action is taken, yet you keep seeing the same problem coming back. It has been their MO for a very long time now.
Or in other words, they’re not obligated to tell you the truth, if anything at all. It’s all about pros and cons with companies in situations such as these, and what carries the most pros.