At that hour, I imagine most people would use the main door of a hotel to enter, especially when they aren't actually staying there.
And maybe it doesn't scream professional, but it doesn't scream amateur either, to me. Stopping for snacks suggests that he was ready to wait awhile, because the victim was apparently there hours before he was due to speak - so that would imply that the shooter had either been well-briefed on his habits or that he had some help - perhaps from someone at or near the other hotel who let him know when Thompson was on the move so he could get into position.
The bike is also a pro move, IMO, because having spent 10 days in the city, he'd have to know that being stuck in a car in traffic or confined to a subway is not the best escape, and one can only move so fast on foot.
The police have apparently assembled more than 200 images of him around the city, and yet given that it's been 2.5 days now, there's every chance he's long gone by now.