H202 provides the body the ability to destroy organisms through an oxidation process. I have never read anything to suggest it could worsen candida overgrowth. If it is orally ingested in very large and unhealthy amounts resulting in dysbiosis, then perhaps indirectly it could worsen candida overgrowth. I'm interested to see the study you are referring to.
Taking large amount of garlic or H202 can cause undesired results. The symptoms you describe are the result of too much garlic and/or H202 being ingested. All things in moderation is always best.
I was greatly helped through the h202 inhalation method. I still use it now. Anyone with a serious candida overgrowth problem cannot be cured by this alone, but it is a very potent and powerful part of the process.