What is claimed is  

 -The idea that Hyppasus of Metaponte has discovered incommensurability is not usual. Neither Neugebauer, not Knorr think that's true. Hyppasus is supposed to be an early pythagorician, Neugebauer thinks that discovery happend during the first quarter of the fourth century (see  second foot note and Knorr before -450 (p 37 of the reference I gave for Knorr could be checked on google book). 

 -If Hyppasus is the author of the discovery, then it is with a pentagone and not with a square (with the golden ratio and not with square root of two). This could be checked by Von Fritz, not accessible under Google but this fact is so well known that I am sure it could be checked with google in english. 

 -Hyppasus is sometime credited of the discovery, but never of the proof. For instance, p 37 you can read that for Knorr discovery time is sometimes before -450 and proof happend after (a decade or more).