There are certainly indications that the genre is slowly growing!
But that said, my guess would be that the adventure category in the ESA reports includes everything adventure-esque, from traditional adventure games (point & click etc.) to Zelda, Tomb Raider and Prince of Persia. Maybe even a game like Assassin's Creed fits in that category.
It's not uncommon these days to categorize like that. So personally I wouldn't put too much weight on those numbers, when the focus is traditional adventure games. The real number could be less than 1%, hard to tell
