Some puppies are a little more timid than others, and some puppies will pick the strangest things to be scared of. Its definitely very common for puppies to be scared at that age. When Piper was that age, I carried her outside and didn't put her down until she was in the exact place where I wanted her to go potty. 1, it helped avoid accidents on the way outside 2, there are tons of dogs in my neighborhood, and I didn't want to have a surprise run-in we weren't prepared for, and 3, I didn't want to overwhelm her
My childhood dog, Buddy, was terrified of grass growing up, because we grew up in a desert area out west, and the breeder didn't really have grass. So when we brought him home and took him outside for the first time, he was totally scared of that tall green stuff in our yard!
Your puppy is in a totally new environment, with lots of new sounds and smells, that can be overwhelming. I'd make sure puppy isn't alone when you take him outside, and that you are very close by, to make him feel more secure. Taking treats with you, just to provide positive reinforcement of activities you want him to do, like walk on, or even just inspect grass, can help to. It helps them associate scary activities with positive things. Piper is a more timid pup, she would get nervous around strange objects (recycle bins, strollers, the mailman cart, furniture that people leave on the side of the road), especially at night. At first, I always had treats with me, to help her be more comfortable sniffing and inspecting those strange objects. I also stayed within a couple feet of her to help her feel secure.