It's not in and of itself a bad thing per se. It's not as bad as vomiting all over the Prime Minister for example or getting a kiss from the Saudi King.
But my understanding is that the President isn't supposed to bow to anyone. In any event the image fits perfectly into an ugly narrative about the President which his political enemies have been honing for quite some time. He has to be careful about such things.
To paraphrase Vito, "Men, women and children can be careless, not the President".