It is impossible to tell how much time has passed in the Pokemon world between these two episodes, but I will reply with it is unlikely that Ash has done anything important in that time.
There is not normally much continuity between Ash going to different regions. He takes Pikachu, and sometimes one or more of his other Pokemon, and goes off to explore the new region. There doesn't need to be much continuity there for that basic premise to work.
It probably seems more so than normal in between the end of Sinnoh and the start of Unova, because the writers made a definite effort to cater to first-time viewers. The voice over of BW001 states Ash's age, that he wants to become a Pokemon master, etc. It is like a new beginning for the Pokemon anime. It is also probably why people who watched the earlier versions of the anime hate the Unova version - because Ash makes a lot of rookie mistakes, and really should know better by now. But his intelligence and knowledge seems to have gone back to how he was during the very first episodes of the anime.
This making a new start is also shown by having no old Pokemon in Unova (until you get to Eastern Unova, anyway) and (in the games) having the route numbers starting from Route 1 again.
