If it sounds unbelievable, that's because it isn't remotely true. DDR5 is 13% more efficient than DDR4 and has 4 times the max die density. 256GB broken up into four 64GB sticks would use about 8 watts.

This person make insane claims about power all the time. They claim nothing will surpass old raspberry pis and intel atoms in efficiency, that nothing will surpass 1 gb networking due to power constraints (even though it all has existed for well over a decade) and even claim that certain video games won't be playable in the future from power constraints.

It is best not to think about it too hard.

64GB DIMM are probably brittle.

The 256GB I mentioned was industrial server memories built to last.

None of what you are saying makes sense. Why do you think any of this is true?