I don't think aliens being here implies FTL travel. If we're assuming that there's such a huge thing we don't know, it seems equally likely (or even more likely

I don't think aliens being here implies FTL travel. If we're assuming that there's such a huge thing we don't know, it seems equally likely (or even more likely) to be a surprising surprise. We're assuming that they got here in a way we didn't anticipate, so why assume that it's via FTL travel?