From Corsair

>> DDR5 technology comes with an exclusive data-checking feature that serves to improve memory cell reliability and increase memory yield for memory manufacturers. This inclusion doesn't make it full ECC memory though.

"Proper" ECC has a wider memory buss, so the CPU emits checksum bits that are saved alongside every word of memory, and checked again by the CPU when memory is read. Eg. a 64 bit machine would actually have 72 bit memory.

DDR5 "ECC" uses error correction only within the memory stick. It's there to reduce the error rate, so otherwise unacceptable memory is usable - individual cells have become so small that they are not longer acceptably reliable by themselves!