There's a difference between not being designed for something, and being designed to prevent something.
HLS isn't designed to prevent saving, it's just optimised for streaming.
The GP stated that hls makes it harder to download and store videos which is mostly a dubious claim, but even if it were true, in most cases where it’s used this is (if only hypothetically) a benefit since major stream providers generally don’t want their streams stored. The reply sounds appropriate.