I got into a double battle in the normal grass. Is this a glitch?

Question

I was on route 3 near wellspring cave in Pokemon black, and while in the normal grass, I came across two pidoves!

Is this a glitch? You can't find a double battle in the normal grass, right?

Answer 1

You can find darker grass in 5th gen games. In these grass patches you will find Pokemon of higher level and you can find two Pokemon together sometimes and you fight them in double battles. If you look at the patch of grass that you found the two pidoves, you will notice that it will be darker than other grasses on the route.
Source: http://bulbapedia.bulbagarden.net/wiki/Dark_grass#Dark_grass