There are apparently rad-hard DDR4 chips these days so this is patently false. SpaceX used to talk a lot about substituting rad-hard components with triple redundant regular x86 years ago, that's true.

I think I've also seen someone mention that the cost and power benefit of substituting rad-hard chips with garden variety wean off fast once the level of redundancy goes up, and also it can't handle deep space radiations that just kill Earthbound chips rather than partially glitching them.