“Most” of the volunteers preferred Sparkle is a generalization true of the entire group of volunteers. But it’s not necessarily true of each of the five smaller groups. So one of the groups might have preferred their competing cola over Sparkle.

The conclusion only concerns whether Sparkle elicited a more favorable response during the taste tests in the study. The conclusion doesn’t concern whether people would buy Sparkle.

The conclusion only concerns the comparison between Sparkle and “the competing colas tested.” It doesn’t assert anything about colas that were not tested in the study.

The argument only concerns the response of Sparkle Cola vs. the competing colas based on the taste tests in the study. Whether people might prefer Sparkle for reasons besides taste was not part of the study and isn’t part of the conclusion.

The conclusion is concerned only with colas. So the fact the study didn’t investigate non-colas is irrelevant.