Taste of beer causes chemical reward.
Fragment of a discussion from Comments:Study: Taste of beer causes chemical reward in male brain
This doesn't seem surprising. If someone has enjoyed drinking before then tasting it will begin to elicit a response in the brain as it "remembers" the last time[s]. I wonder if you did this study with people who had never drank before in their lives if you would see the same difference between the sports drink and beer, my guess is there would be no difference and neither would cause dopamine release.