i interpreted that to mean that the person correcting for a salutation like that means that they are trying to schmooze an u/g just b/c they are "in this case" a doctor and in that case, they'll get an u/g all right

I can't blame him for that; its all fine and dandy if you are a doctor (or insert other title) and good for you, but to use it to try to get an u/g, or whatever just b/c one has a difficult profession isn't always going to work or it may back fire and I think that is what the poster your quoted was saying