I just examined it over on Besaid.

This is the skeptic in me talking, but I think it has nothing to do with recent events. Remember how sometimes someone would be able to glitch a retainer to appear in the adventurer's guild at the bell? This may be a glitched node for someone's guildleve.

Supporting that is the lack of a major "shiny" light flare at the top of the node, as what you would see at the actual main node itself in Nanawa. Real aetherial nodes have that shine.

The placement itself is also rather weird, since Nanawa itself is a mid-range underground cavern.