They may be referring to close family members. These are the people mostly likely to offer unsolicited parenting advice in my experience.

That and (though I’m not speaking on behalf of OP) social media destinations like Facebook, where most of us are likely to have had “friends” we haven’t seen since high school and will never see again in person.

The people in my family who smacked their kids aren’t professionals. Plenty of professionals hit their kids though.

Right? Kids are different, but honestly not that different from adults. Just more impressionable, because they are learning the world. And of course less knowledgeable and developed by definition. But they work a lot of the same ways.

Would you make it practice to hit adults??? No? Why are you teaching kids that this is what happens?

It makes no sense.

Of course it makes sense. Pain is the universal teacher. It's why every organism that can move under its own power experiences pain. We are extremely good at learning pain avoidance. We even used to hit adults (and far worse) to get them to behave. So yes, of course it makes sense. Whether it results in positive outcomes is the only legitimate question.

For many of these people, yes. They would absolutely make it practice to hit adults.