Right but the ACM is the ultimate source of the data. They own the conference, the paper selection processes and hence the list of papers. It's hard to argue that this list was compiled without _ever_ looking at the ACM's list. It's a grey area for sure, and you could argue that if you go to the conference and simply observe the presenters and their paper titles, or even just ask the authors "Did you get a siggraph paper in? What was the title?" then that is your data, but by the same logic I can go to the World Series and live-blog a play-by-play account of the game, which would surely get me sued. (Maybe people do this I don't know I don't follow sports, but I know that the leagues claim copyright over accounts and descriptions, regardless of whether they actually have those rights.)