Even back when /dev/random estimated entropy, it was still a CSPRNG. At that time, /dev/random and /dev/urandom used the same cryptographic function to generate

Even back when /dev/random estimated entropy, it was still a CSPRNG. At that time, /dev/random and /dev/urandom used the same cryptographic function to generate pseudo-random bits, random just added some additional fluff based on the claim that it was “estimating” randomness.