I guess it's "so completely" as opposed to "partly completely", and if we have two differing accounts of something, aren't they both false? Well, I'm not touching that one.
But the genealogies are different. We have two different bloodlines through two sons of David--Solomon and Nathan. The question is how they intersect. There are a number of viable theories, and
this one at least has the virtue of simplicity. But without further documentation, we don't really know. And this cuts both ways, because the mere existence of two genealogies is not a prima facie case for Biblical errancy, either.