You're right, to a certain extent.
But let me give you an example. It's probably a bad example with no real application, but it'll suffice enough to explain the general idea.
Let's pretend that you know absolutely nothing about math. Nothing. You know some numbers, and you know that math exists and you're pretty sure it has to do with numbers.
Appleton makes a post that declares the following: "2+2=4. There are no exceptions! Our basic understanding of math from the very beginning has shown this to be true!" This post has 2000 karma.
In the comments, you find a response: "Is this guy trolling our just stupid? Look, I'll humor you in case you've been living under a rock for the past few years. Back in 2012, mathematicians proved that the old system had it way wrong. See, you're looking at it in terms of vectors, when really is that radians that you should be considering. Using the newer equations, you'll see that 2+2 definitely does NOT equal 4." This is the top comment with 1000 karma.
The idea of second opinion bias is that, as someone in ignorance, you will tend to automatically agree with that comment. You don't really know whether or not he's right, but his argument SEEMS really well put together. (An important detail here is that the argument doesn't necessarily have to actually be well made, it only has to seem that way top the uneducated viewer. The actual material of the comment doesn't matter, only the fact that it seems well put-together.)
Further, second opinion bias doesn't necessarily suggest that the second opinion has to be a false one. It only states that an uneducated reader well be inclined to agree with it blindly.