No they were only scanning iCloud email. They were lagging well behind other services in identifying this content, only finding a few hundred compared to millions by Facebook for example.

The system only works with iCloud Photo Library, it needs a server side component to continue the process.

https://www.apple.com/child-safety/pdf/CSAM_Detection_Techni...

This is a very interesting read and personally I think they’ve gone to extreme length to make this system as private as it could be.