I'm guessing they use this alongside CSPRNGs. Would make sense given the theorem that states any random number XORed with even highly-ordered input maintains its entropy.
I haven't yet seen a good argument why it's a bad idea, and part of me thinks it might be a way to get more software using "rdrand" or other insecure sources unmodified.
To the people that just say it's never a good idea and scoff at any reasoning I'd remind them about OTPs. They are a special case related to this principle of XORing two independent sources together where only one input is random and it is proven mathematically to work.