These are UDIMMs, not RDIMMs. As mentioned 32 GB per module (without going RDIMM) has only been possible for about a year.
ECC does not automatically mean RDIMM although presently there are no RDIMMs without ECC functionality. Which makes sense since all platforms that handle RDIMMs usually use ECC (And since Intel is sooo concerned about not confusing customers they cut RDIMM support from some socket 2066 non-Xeon CPUs where running RDIMMs had been possible with ECC disabled).
No Ryzen boots with RDIMMs since AMD disabled that feature in the memory controller of that product line to differentiate it from Epyc.