This event took place at a university's performing arts center. I went to their website, and it turns out this policy was just put in place for all their events:
Performing Arts Clear Bag Policy
Effective Oct 22, 2018: For the safety of our patrons, security measures have been instituted at all Performing Arts venues. We strongly encourage guests to only bring essential items in order to provide a safer environment and expedite guest entry into the venues.
The following bags will be permitted into all Performing Arts venues:
- Bags that are clear plastic, vinyl or PVS and do not exceed 12” x 12” x 6”
- One-gallon clear resealable plastic storage bag
- Small clutch bags do not have to be clear but cannot exceed 6.5” x 4.5” x 2” with or without a handle or strap, may be carried into the theatre along with one clear bag option
Prohibited bags include:
- Purses
- Diaper bags*
- Cases (camera, binocular, etc.)
- Backpacks
- Fanny packs
- Printed pattern plastic bags
- Reusable grocery totes
- Mesh or straw bags
- Duffel bags
- Large totes
*Items normally carried in a diaper bag must be put into a clear plastic bag for venue entry.