There are other true bugs that look like assassin bugs, and even have similar looking proboscis type mouthparts. More importantly, these bugs, like leaf-footed bugs (coreidae, for example) do feed on plants. Old folks are funny. Half the time they are wise and the other half they're entirely off their rockers!
I've never smelled an odor from an assassin bug, but that doesn't mean that some species don't excrete or that some humans don't have better noses than me.