Don't worry about it. I don't believe in bad questions. It was important for the fulfillment of prophecy. 2 Samuel 7:12-16 tells the prophecy so that's why it was so important to give proof of David's lineage.
Ah, I see. You mentioned you have mostly studied the NIV, ESV and KJV, right? Let's have a look at the prophecy in each version, specifically at verse 12:
NIV
When your days are over and you rest with your ancestors, I will raise up your offspring to succeed you,
your own flesh and blood, and I will establish his kingdom.
ESV
When your days are fulfilled and you lie down with your fathers, I will raise up your offspring after you,
who shall come from your body, and I will establish his kingdom.
KJV
And when thy days be fulfilled, and thou shalt sleep with thy fathers, I will set up thy seed after thee,
which shall proceed out of thy bowels, and I will establish his kingdom.
To be honest, when I read your reply, I thought, "Eh, another prophecy that is either self-fulfilling or so vague it can be interpreted in any way", but I was wrong. To me, the prophecy is rather clear on that point: the one mentioned here is supposed to be a direct descendant, in the biological sense, of David, thereby excluding Jesus.
Of course, there's the part where God says he'll be a father to him, who shall be like a son; but if anything, then this part is the one least susceptible to be taken literally. Especially in the ESV, where it says "I will be to him a father, and he shall be to me a son. " This is, at least in the English language presented here, clearly portraying God's intention to be 'like a father to him', meaning taking the
role of a father, not being his actual biological father; as it was made clear before that David will be the biological ancestor.
And while this latter part might be a translation issue (as it is a figure of speech and rather implicit), I think the former passages which I emphasized in bold in each version is so explicit that it cannot have been an error, could it?