People like to trot this little gem out when there is no evidence for it. The only sources for Helio having any judo rank is a book by Robert Hill and Kimura's autobiography. Hill's book claims that Kodokan records show Helio as 3rd dan, however there are no sources listed for this claim and I have found no other corroborating sources. Hill's book is pretty thin on scholarship all around.
Kimura's "My Judo" refers to "Helio Gracie, 6th dan" but it could have been a mistranslation of Kimura's original Japanese, a misunderstanding on Kimura's part, or, shockingly, a confabulation on the part of the Gracies. Either way, no one has produced a copy of Kodokan records that mention Helio Gracie.
Several people who would know better than anyone on this board, including Rorion, George Medhi and Francisco Mansour have flat out said that Helio never studied judo at all.
If Helio did study judo, who was this mysterious Japanese judoka who taught Helio for years and years and has remained completely anonymous?
Helio talked a lot of shit about judo and absolutely believed in his brand of jiu-jitsu to his core. I find it hard to believe that he'd go train judo in secret, be dedicated enough to earn a 3rd or 6th dan, but still bad mouth it in public.