Let me quote the important part, emphasis mine: "...majority of players, after trying both playlist types, chose to stick with Open Weapons...". So not only that the players they are talking about seen the Open and Close options, they even tried it and then decided to stick with Open. In other words, they are talking about players that tried both modes, not all players, so there is just a very little or no bias. I think their statement and reasoning is pretty clear.
I think you ignored the fact that I also said there were more game modes available to open weapons. Even I, who prefers closed weapons, played a good bit of open weapons because of the game modes like rush or breakthrough. For example, in the beta conquest and breakthrough were combined under one playlist at one point for closed weapons, and I couldn't for the life of me get a closed weapon breakthrough match so I went into open weapons breakthrough just so I could play the mode.
It depends what playlists they measured, when, and how - I assume that the stats were made against relevant playlists or there was some compensation as any sane person would do, for example (as far as I remember) there were Open conquest and Closed conquest in the first beta week. Same mode, same maps, the only difference was open vs closed weapons (which also means no bias for these lists).
