In general a question belonging on another site is in itself not an appropriate close-reason. The primary question you have to ask is, is it on-topic on this site? Granted, the specific question is indeed not appropriate for our site and has been closed as such. Though, I strongly doubt it's on-topic for either ELL.SE or ELU.SE, though, but let's concentrate on the general problem for now.
Yes, the migration option is directly part of the off-topic close-reason. That is a bit of a design flaw (and quite a legacy relic really), suggesting that being on-topic elsewhere could be a reason for it to be off-topic here. But, it's really not.
Anyway, so what is that option for and how can you suggest a question for migration. A site can indeed have other sites there in addition to just its own meta site. But these options have to be activated manually (normally by SE employees called into action by the moderators after corresponding meta discussions deeming it a good idea). However, this only happens when it is necessary and seeing how we migrate about a single question every 3 years to ELU.SE, it's simply not worth it.
The general approach nowadays, especially on such low-frequency sites like us, is to leave migrations to the moderators and not have a ton of different sites there, since as described above this can have the disadvantages of encouraging overeager migration close-votes just because a question might "fit better" somewhere else. If the question is off-topic here, then close it as such with an approrpiate reason. This motivation is also elaborated in the answers to this related question.
Then we can think about possibly migrating it to a place where it is on-topic, but we'd rather leave that to the responsibility of the moderators who can very well deal with the work of ~1 migration a month. You can support the moderators and/or the asker in doing so with helpful comments or even custom moderator flags. However, when doing so, please make sure that it is really appropriate on the other site (or at least explain in the comment that you're unsure about this). Having the asker reask it on another site only for it to get closed again there too is a really unpleaseant experience for everyone involved.