What would cause bubbles in confit garlic stored in oil?
A jar of garlic in oil at room temperature (whether or not is was simmered first - pressure-canning might be different) is indeed a ripe environment for botulism. I'm not clear why you would store the product at room temperature if you have even a passing familiarity with botulism? If you store garlic in oil, it should be refrigerated. The second link includes a specific mention: 


  The same hazard exists for roasted garlic stored in oil.


Chuck it. The fact that there could be benign fermentations going on is not worth the risk of the non-benign bacteria and resultant poisoning.