I didn't mean reporting things that you wouldn't consider a bug and just close. FWIW tho, "Pasting War and Peace" is actually a good test case. While it is unlikely you need to support
that size in your inputs, testing such extremes is still valuable security testing. Quite a few things are security issues, even though regular users would never find them. Like permissions being applied in the UI only. Actual users wouldn't find out that the BE doesn't bother to actually check the permissions. But I damn well expect a QA person to verify that!
Was I meant though were actual problems / bugs in the area of the product that your ticket is about. But that weren't caused by your ticket / have nothing to do with that ticket directly.
Like to make an example, say you're adding a new field to your user onboarding that asks them what their role is so that you can show a better tailored version of your onboarding flows, focusing on functionality that is likely to be useful for you in your role. While testing that, the QA person notices a bug in one of the actual pieces of functionality that's part of said onboarding flow.
A good QA understands and can distinguish what is a pre-existing bug and what isn't and report it separately, making the overall product better, while not wasting time on the ticket at hand.