I wonder if they don't mean "between systems".
I thought it meant like keep things as local as possible. Like within the same process, within the same machine, avoid going through the network because staying on the processor is always the fastest, going to ram is next fastest, and if you need to communicate across the network it is always slowest
Performance is and always was something dependent on the domain rules. You don't start architecting for performance before understanding requirements so why make it a pillar of all architecture.