The presence of lactate in German beers is widely reported in analytical reports for those beers. Lactate is also consumed to some degree by yeast. I have no idea what the metabolic products of lactate consumption by yeast is. But all of this does suggest that there could be a flavor impact to beer, even when the lactate content is below 400 ppm, which is the popular taste threshold reported for the average taster. Be aware that some tasters can perceive lactate at higher and lower levels...remember that 400 ppm is for the average taster.
I tried to estimate the water volumes used in the trial and came up with about 3.5 gallons of mashing water and 4.5 gallons of sparging water. Malcolm will need to confirm for me. At those volumes, the resulting lactate content in the overall beer is more likely to be around 250 ppm, not 400 ppm. Users of the supporter's version of Bru'n Water know that that program reports the anion content of the various acids used and also warn when the content might be at or above the taste threshold.
The other concern I have is that the sparging water was only taken down to a pH of 6.0 and that suggests that the amount of alkalinity remaining in that sparging water is about 50 ppm (as CaCO3). I generally recommend bringing the alkalinity down to about 25 ppm.
All of these results do suggest that my original hypothesis that lactate can add a flavor 'nuance' to beers brewed with lactic acid...even when below the taste threshold of the average taster. I've heard some brewers say they hate even minor additions on lactic acid, but most drinkers seems OK with it. When sensitized to it, I expect that many tasters could detect it at lower than the average content.