I don't know the actual term but it's a fetishistic response from watching too much hentai. This happens with real porn but more with cartoon sex because the visuals are less detailed and more figurative. As you said "animation tends to exaggerate certain features to indicate emotions". Over time the viewer's brain learns to associate pleasure with specific drawing styles or visual tropes. (btw same problem with furries, who spent their formative years looking at cartoon animals with giant throbbing penises)

So when this pervert sees anime that invokes those same cues (blushing) they get turned on, then get angry at themselves, and project that angry perversion onto other viewers and the creators who had no such intention.