Well it has to be INVESTIGATIVE at the very least - I don't think Gozilla and Mothra typically solve mysteries. (Though I'll admit, I'm not super informed of Kaiju lore.)
But yeah, I suppose it's true that it might not mesh well with a module that assumes you're playing a power fantasy game. But I suppose when they wrote that line they were more thinking of stuff that came before, your call of cthulu mysteries or even generic mystery modules.
EDIT: Wait, I was basing this conversation off of what it says about using other Modules in the BOOK ITSELF. I see now you're responding to the line above in the itch post. I agree the wording might need modification.