Any thoughts on how load conditions could have lead to ID lookup being messed up?

Wyze (the smart home company) recently had a security incident and sent an email explaining it. However, something in the explanation caught my attention and I've been racking my brains on how this could have happened… any thoughts? Here's the relevant text

The outage originated from our partner AWS and took down Wyze devices for several hours early Friday morning. If you tried to view live cameras or Events during that time, you likely weren’t able to. We’re very sorry for the frustration and confusion this caused.

users received thumbnails from cameras that were not their own and 1,504 users tapped on them. Most taps enlarged the thumbnail, but in some cases an Event Video was able to be viewed.

…

The incident was caused by a third-party caching client library that was recently integrated into our system. This client library received unprecedented load conditions caused by devices coming back online all at once. As a result of increased demand, it mixed up device ID and user ID mapping and connected some data to incorrect accounts.