I checked and see no sign of glue. Then again, the glue may not be visible anyway.
It appears based on the break that the joint may have had been partially glued. One part of the joint (without the glue) was able to flex a bit and the other part (with the glue) was not, causing a split in the wood.
No biggie though. If it weren't under warranty, I would simply glue it back into place.