While I agree with your argument about the source, I’ll nitpick your example.

external stimulus does not mean something feels something. just because you flipped your light switch doesn’t mean your lightbulb gets angry and glows. same for living organisms.

IMO a better example is how fish can be aggressive to other fish, and this can cause psychological reactions that can be observed; scale loss, lethargy, starvation, increased aggression, death. IMO if an organism can exhibit observable psychological responses, it has the capacity to feel.