The two tabs things is strange, but it is normal to get get points for giving out BAs. You get 2 points for selecting an answer as best, so by selecting the answer as best twice you got 2 points for both of them.
If you are worried about people doing the same thing to get points on purpose, don't be. You only get 2 points from selecting BA, so you would have to be really, really patient to get a load from just that. And I don't think trolls are normally that patient.
So in conclusion, you don't have to worry about it. It's supposed to give yu points, and 2 isn't a lot anyway, so it won't be a problem.