>There are other possibilities...
While it may not apply to this specific situation, I have observed multiple instances of swarms re-bivouacing before selecting a final cavity.
Similar to a Russian Scion (with all due respect tol all Russians everywhere), the swarm may have been looking for a new place to cluster and the location and scent of the stack was appealing.
When the drawn comb was made available to them, they couldn't resist.
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