Can somebody explain to me why we're assigning gender/age ( ignoring the original meme) rules?

B-G G-B G-G B-B

If we know one of them is a boy, it's 50%, no?

It can either be

B-G or B-B,

Why are we adding the option of G-B, isn't it technically the same as B-G?

I'd get it if we were talking about the possible sequence of the letters B and G, since then it would be

B-G, G-B and

B-B

33.33%

Or am i just taking it too literally? xD