Eating at a steak house without the press has nothing to do with his job as the President. Good for him for standing up to the media. He should be allowed to do things with his family without always having to take the press on an outing. The press just can't handle not being the center of attention.
Donald Trump has one thing on his mind, and that's making sure that Donald Trump looks great. Ditching the press pool in order to talk to actual Americans and give them a crazy story to tell their friends makes him look great to his base. They love it when he tweaks the nose of the media.
Trump should have addressed the press pool, so he can reach more people when he speaks. There's a lot of upset surrounding his presidential win, and in order for Trump to get people onto his side, he will need to address the public, not just those who already voted for him. By ditching the press pool to speak to people in an upscale restaurant, some people may see that as his preference for working for the rich, rather than for all of America. This move will not likely lose him much support, but it is not helping people warm up to him as our new presidential elect.
It is my belief that Donald Trump made a mistake by ditching the press pool. This action demonstrates that Trump is uninterested in media transparency and prefers secrecy so that he can hold two positions: one in public, the other in private. Further, Trump's decision will only confirm his opponents' criticisms and fears that he will act in an authoritarian manner.