ROM Sudden Bee Death

I just read this article which reports on the sudden death of the 20,000 bees within two days at the Royal Ontario Museum’s biodiversity exhibit, even though they had appeared healthy.

They think poor ventilation, disease or the lack if worker bees could be the culprit.

I don’t raise bees myself, so I don’t know how common such problems are with bees.  I would appreciate any feedback from experts.