I think the concern was with mfg. cross contamination - the boxes being next to eachother probably brought the possibility to mind.
They've been recalled over the years, too-- so it's VERY likely that they share a manufacturing line. I'll also add, here, that our personal experience suggests that ANYTHING "JELLO" brand probably shares a
packaging line...
because my DD has very consistently reacted to even very small amounts of Jello-- not even the pudding (which she's never had, to be clear)-- even jello-jello.. This is an N, here, of at least seven or eight, and some of those reactions have been grade III or more, and to a single bite of something.
She is very definitely NOT allergic to food colorings or gelatin, but she
is highly allergic to pistachio and cashew. So I think that for someone with a known pistachio allergy, severe rxn hx, and a demonstrably low threshold, this is probably a somewhat valid concern. It's why we don't use anything in the Jello line.