Hmm I have no idea what its supposed to be but it feels like it should be a bard feat instead of a general feat.
If this is the case, no problem, but I see no reason (in context) for that.
Lingering song and extra song appears in the general feat screen. As mentioned above, once you unlock barbarian rage, the rage feats appear in the general screen. Metamagic feats, once you unlock them, appear in teh general feat screen.
I do believe that a very narrow feat selection is locked under classes (weapon specialization, martial supremacy, etc.) Unless it is a class+level locked feat (like the combat forms) there is no reason to not allow a bard/ftr to grab a song feat in the fighter level.
But, again, the bug is the incongruence between the wiki and the game... one of those will have to change. Then we can discuss the balance of the situation.
Edit to put a picture:
The feat is general in its description, therefore, it is a bug of the feat and the discussion of balance is completely valid, but another thing.