You're right, but the pollsters who polled in the Deer Hunter and Red states were (IMO) some of the more screwy pollsters nationally. eg, Monmouth and Survey Monkey polled Wisconsin and got that completely wrong, too. Most pollsters who were on the money didn't poll individual states.
But my argument stands: I don't think anyone will be able to tell much about Trump from national polling for the next 4 (or 8) years.
FWIW, President Ulysses Grant probably didn't have very high national approval numbers, either.
Polls aren’t news. They are opinion. Polls can be easily cooked to say whatever you want them to say.