Yeah, I have no idea, but also no reason to not trust the Bluelab EC meter, especially since it seems to match the other 2 cheap ones I own and is also properly calibrated. I guess it's possible that the bag of Maxibloom I have slipped through QC. I have a second bag (from a different vendor), but I haven't opened it since I hate to do that unnecessarily to avoid any clumping.
I've been using water that's filtered, or dehumidifier condensate both of which are reading 0ppm/0EC on all meters as well.