To be fair, while bugs and other insects don't have lungs, some arthropods do. The differences among arthropods, insects and bugs aren't exactly common knowledge.
Also, IIRC, some fish are more closely related to us than they are to other fish, making it impossible to biologically define a category of animal that includes everything we call a fish but doesn't include us.
I’m less bothered by that person not knowing and way more bothered by them just being so confidently incorrect. Doesn’t take long to just look it up yourself. Unless the whole post was an educational setup?