This is a (lightly edited) composition of the comments left above by @Scortchi, @whuber, @Glen_b, and Roland (I am marking this answer as CW). I believe they fully answer this question. 

> There is no practical distinction between "focus on" and "about". Migration occurs when the question is likely to be considered on topic at the destination site. Closure occurs otherwise.
>
> In practice we often close questions just because they're not good enough to migrate to SO. Many such lack a [minimal, complete, verifiable example](https://stackoverflow.com/help/mcve). Not every programming-related question is on topic at StackOverflow.
>
> At the least be sure you're familiar with the requirements of their help/on-topic before trying to migrate there. If you don't feel qualified to judge if the question is of sufficient quality for the migration destination, then don't vote for migration.