It'd be lying if he were to say "we have 100% POSIX compliance." Very few OS projects can claim that. It needs to also be version-qualified, as there are several POSIX standards and even Windows can claim compliance with some of the versions.
My point is that this information of the current state of the project does not belong in the introduction to the project. The fact that it is a Zero-Point-Something version number is information enough that the project is incomplete.
SpaceX "...DESIGNS, MANUFACTURES AND LAUNCHES ADVANCED ROCKETS AND SPACECRAFT". They don't add caveats about completeness or design flaws or anything of that sort in their introduction.
And my reduction is just a call-out. The introductory section of the site is three paragraphs and a sentence long. It's not an introduction at all, at that point. All of these extraneous details are specifically making the introduction less clear, not more.