What you say is technically true but is a bit of semantics. I just meant wet materials look shinier, which makes them appear more reflective and is another way of showing normal map details. You do see the effect of more normal map detail because of the increased contrast and the sky reflecting off the top of details. It’s not about the lighting response of the basecolor at that point as you point out, its more about the more noticeable reflection details.
That grass overcast scene is nice. Notice he has pretty high quality AO for the grass, and even the ground looks to have some undulating in the lighting detail. Its unclear if some of that variation is painted in or all responding to lighting. If its responding to lighting then he probably has the HDR set up so that one side is a bit brighter. But it does look to have subtle AO baked in as well. Its nit picking but I feel like the normal map on the rock mesh is too strong for that overcast environment, or there isn’t enough bounce on the underside details. Maybe the lichen is just missing subsurface which would help a lot.