They may be indicating a possible digestive intolerance. Raw onion and garlic is difficult for me to digest (allium intolerance?), cooking helps but still can be difficult in high quantities.

I'm trying to parse that sentence.

As opposed to episodes of something else? Was something reported before or after the intervention? Is that all they were told to report? Is it good? What???

In the context of the rest of the sentence, it means that only flatulence and not other symptoms like intestinal discomfort were reported.