Regardless of where it was published, there's really no basis that I can see in the work itself for this being tagged shoujo-ai.
Even if one assumes that we are supposed to assume they're probably a couple or something from its publication context, I'm not sure that rises to the standard of relevance for the tag.
I mean the internet seems to think that it is shoujo-ai, so I'm hesitant to take down the tag myself, but there's barely even homoeroticism in this.