This is actually a common thing right now, but information is being censored by the big processed food suppliers. For more info and to see if your grocery store's supply might be affected, Google "Blue Waffle uncensored"
Yeah, plus this likely didn't happen. They probably took it out of the package, saw the mold and made a joke. I'm not saying it definitely didn't happen; the universe may not be infinite but our ability to make bad decisions/mistakes certainly is.
In my 51 years I've never seen mold grow in a freezer. Preferably a mycologist would chime in to clarify if there are any molds that grow under those circumstances.
My guess is that 1) there was a supply chain issue where the product wasn't held at the right temp long enough for it to mold, then continued on its journey to a home freezer. Or 2) "Oops! I bought too many groceries and can't fit everything in the freezer. I'll just throw this box in the fridge (and proceed to forget it exists.)"
The freezer probably isnt always that cold. i.e its easy to accidentally block the vents near the back and if that happens, it screws up the temperature of the interior of the fridge
Tbf to OP, I once had a full serving of moldy rice and didn't notice until the following day because a) I didn't look very closely, and b) It didn't smell/taste off or weird.
That assumes theyre always frozen. Accidentally blocking the vents, a failing fridge, a slightly cracked door, all can cause the interior to not be as cold as you think it is.