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Note that "lock-free" is a technical term that has a very specific, precise meaning (implying that the user of the structure does not need to use locking explicitly).

Even in single producer single consumer scenarios you need locks for multithreaded/interrupt use if you're not properly using atomics and proper fences.

You may need a lock if you have operations that are not atomic, even with a single writer, as a reader could find an inconsistency.

This seems unnecessarily pedantic. Lock-free conventionally implies concurrent, otherwise it's meaningless.

Lock-free doesn't mean "doesn't have locks". It means "doesn't need locks to be used concurrently".