Concurrency didn’t necessarily require threads. Concurrency is not a difference in how you use threads, its logical computer science concept. Parallelism is a physical property and parallelism is almost always concerned with doing things a faster by doing them in parallel, concurrency can be done for other purposes (eg to not have long running tasks block work). All parallel programming is concurrent but not all concurrent programming is parallel.

The distinction matters because the focus is different: they’re different topics. With concurrent programming you deal with synchronisation and topics like lock-freedom and wait-freedom. In parallel programming the main focus is about work distribution and scheduling to process it faster.