Are you certain that it is saying you reached rank 2? With cards that have rank rings, Destiny gives in game reports upon getting certain progress milestones towards the next rank. When you actually achieve a new rank, it will not give an "a/b" stat on the banner announcement you see on screen (a=milestone value; b=rank up threshold). An example would be Kills in Crucible as a Hunter: Rank 3 4500/5000. This would mean 500 more Crucible kills as a hunter would be necessary to achieve rank 3. On the other hand, the final message would simply be Kills in Crucible as a Hunter: Rank 3. This would indicate actually achieving rank 3.