I had a very reactive greyhound. His name was Andy. He even tried to kill a galgo in his first foster home. He was the attack first, ask questions later kind of dog.
I walked him regularly and when we met other dogs I kept him behind me, turned him around so they didn't come up front. In canine behaviour it is very impolite towards a dog and look it in the eyes. I always say it is like jogging into a group of real mean bikers and tell them they are ugly as sh... Just not the best idea.
A few weeks is nothing. Your new dog is getting used to everything around him. I would walk regula