I think some of these are correlational rather than causal. For example, the kind of people who love classifying birds are probably already people who love and are good at memorizing things.
#2: what kind of video games? PvP shooters? Grand strategy? Reflex? Detective games? Story/adventure games? Minesweeper? What about non-grid-based trivia/vocabulary games, or open-ended word games without clues, like Scrabble?
The study says they randomized a subset of the available cognitive games for each game session, could the decreased performance be due to the more sporadic focus on any given skills? Maybe some of the trained skills weren't especially helpful for memory.
Or maybe the specific cognitive games they used were just bad? The only detail about them in the study was that they "included memory tasks, matching tasks, spatial recognition tasks, and processing speed tasks." I don't know if it's similar stuff, or how fast they let the game difficulty scale in the study, but I've tried a couple of those brain trainer apps. They started out trivial and boring and scaled up slowly, and some of them were basically just brute force puzzles. Not particularly mentally strenuous.
I don't see a control group who did neither of them, either. So are both crosswords and cognitive games good but crosswords are a little better? Or do these cognitive games give just as much benefit as watching Family Guy?
I'm tired of these very specific studies being wildly extrapolated out as "video games bad." Video games are an extremely diverse medium, it's like saying reading is bad because you only studied gas station tabloids.