Garchomp + Altaria was hyped up a lot. As CrystalEyeMonster said, the player (Yuta Komatsuda) was the one who had the skills to take it all the way to top in the Spring Battle Carnival tournament.
Now about deck lists from Japanese blogs it really depends on who you find. There is those who build decks just to give out a concept and those who performed well with a deck and have the backings to say that they did well with the deck (Sometimes, by the same deck builders who gave out concept lists with some minor or major tweaks). For the most part I've been able to discern blogs who have great amount backing to their deck lists (which many players do share most of the time) with results to those who just play the game to have fun without the worry of winning or losing. All the players I do follow now would probably equivalent to our Master division players.
Now about the tournament scene from Japan. Sure they have a different tournament structure, but remember that particular tournament structure we all know is used for Battle Carnival tournaments which happen twice a year (Autumn and Spring). Now from what I can tell and understand their Gym Challenges are very similar to our current Fall Battle Roads structure. 30 minutes to play (20 minutes in 30 card deck Gym Challenges). Since their only way of getting players to Worlds is through the Spring Battle Carnival (afaik), their tournaments tend be more lax in comparison and smaller in numbers.
When it comes to discern decks, people first threw Hydreigon + Darkrai EX to the side or bothered to even bat an eye at it. Then, I started to share a lot of what was going in the Spring Battle Carnival at time to support the deck thanks to several Japanese blogs which boomed up the play of the deck for our current metagame. Even now, people still ask questions and doubting decks like Blastoise + Keldeo EX and cards like Landorus EX about how it did in Japan because players there are already playing our upcoming City Championships metagame. For the people who are asking this mostly just them wanting to have a good mental state of what to expect.
As far as what are surprise decks, both Garbodor and Durant were already being played when the sets for them were first released in Japan. They didn't get played to the same extent as they did internationally. Sometimes, the format were they being played at the time didn't do well for them (Durant was played in the HGSS - NVI format which had plenty of support for the deck and players willing to play the deck, tweak it, and work on it). Garbodor was an well aware of deck in Japan. Yuta Komatsuda opted not to play Tool Scrapper in his deck because he figured the deck would see less play in the Battle Carnival tournament. Outside of the Battle Carnival, I've seen Garbodor being played plenty in Gym Challenges' tournament reports.
