Two points:
1. Encrypted data is not hidden. You still know that there is data, it's just in a form that you can't understand. Just as difficult higher-level math isn't "obscured" from a non-mathematician (who knows that it is math, but can't decode it), encrypted data is not obscured.
2. You could make the argument that the data is actually hidden, but the fact that data is there is not hidden. This is pointless pedantry, though. It is both contrary to the way that everybody uses the word and stretches the meaning of the word to the point that it's not useful. There is a common understanding of what "Security through obscurity" means ( https://en.wikipedia.org/wiki/Security_through_obscurity ) and interpreting it far beyond that is not useful. It simply breaks down communication into annoying semantic arguments. I enjoy semantic arguments, but not tedious, pedantic ones where one person just argues that a word isn't what everybody understands it to mean.
More specifically, it's about WHAT is being obscured. "Security through obscurity" is about trying to be secure by keeping the details or mechanisms of a system secret, not the data itself.