I don't think it solidifies anything to be honest.
First, these designer's definition of "fake" might just be something that isn't approved by them yet is still made within their walls. Outright fake would mean being produced by a 3rd party, and even though we have seen bootleg 2x4 bricks that are nearly identical recently, I have to consider further info. The 2x4 mold is a rather simple one to copy, but minifig pieces? Scale wise some of the details (internal stamps more so) are just too precise to be reverse cast and made a mold of IMO, and there are several number stamps used on the hips and legs alone. That means that several copy molds would need to be produced...though I do suppose taking the time to 3D model the pieces, print them and then cast them would be the process to follow.
Looking at the images I took for the analysis, the tiny differences here and there for the ABS figs shows inconsistency, so it doesn't seem to me if they were bootlegged that it was done by the same source. Also interesting that they were released as pairs, and the 2nd set (bright green and orange) have the biggest glaring inconsistency with the hip number stamps being rotated 90 degrees. If someone bootlegged this then that is quite a big mistake, which hasn't appeared since, but at the same time I have never seen an official Lego hip with this detail...so it might be safer to assume it was a bootlegger mistake. Still, actual Lego hips and legs have varied in their stamp detailing/scale over the past years, so I can't for sure say that using that as an identifier is accurate. If they were made internally as "nightshift" someone might have access to these different versions (though I would assume molds are retired and/or locked away after not in use anymore). Also seeing the Lego stamp on the neck being rotated 180 degrees in comparison to the internal chest stamps between the PC and ABS is another inconsistency, but it is possible newer molds for solid parts did actually switch the position I suppose. I've never cracked open a normal torso to see if these stamps exist within regular figs, so I can't be certain.
To be honest, I can't draw conclusive evidence due to too many variables along the Lego production time frame to say whether the ABS figs are fake, and if they are they are damn good. Still, I won't believe anything until word comes officially from Lego themselves, not some designers.