I struggle to see it as anything else other than presumptuous and rude.The thing about cooking (as opposed to most other creative or craft activities) is that cooking is something that most/many people do as a day to day thing. Therefore, some think they are qualified to interfere 'hands on' in the process when others are cooking. To them its a normal thing to do this as they don't see as your personal creative process.
If you compare this to (for example) landscape painting or knitting, I think it unlikely that many 'visitors' would be so audacious as to pick up palette and brush and start altering the painting you left on the easel or unpick the knitting you left in the basket and knit a few more different rows.
If one of my sons is struggling with something they‘re cooking I’ll offer help, if they turn that help down then I’m good with that, even though sometimes it may irk me to see food being cooked badly ultimately it’s about basic respect for another person.