Great question. As you noted the guide had native knowledge of that environment which helps a lot. In my local environment (temperature / boreal forest) I'd be decently equipped to find water in a local forest that is new to me because even if the exact area is new it is not completely unfamiliar. I have a general feel of the terrain and indicators, and I have a habit of checking topogaphy maps (if not also bringing them with me) before venturing into a new area.
My local environment is more like rainforest (~1m precip/yr) but what I'd look for actually overlaps a lot with the question you linked to: Finding water in the dry wilderness I'll zoom in on the two primary guides to water I'd refer to in a new area:
Water loving plants and environmental indicators. This is both large scale and small scale, for water sources large and small. On large scale, certain trees and forest types have a tendency to grow in wetter areas, so if you can see these creatures in the landscape they may indicate where you can find water. In my neck of the woods, sparse patches of mainly evergreen forests and some of the following hardwood species indicate wet spots: Yellow Birch (Betula alleghaniensis), Black Birch (Betula nigra), Red Maple (Acer rubrum). As you wander riverside areas, what forest types do you see most often (forest type as in, 3 most common species in the area)? Are there any you mostly see only near wet areas? For small scale, I'm talking about specific plants that retain lots of moisture. You really need to know these plants in advance, or at least know what plants are toxic and indicators of local environmental quality so you avoid harm while exploring plants you're not sure about, and as in any case, where you get sustenance from is susceptible to environmental quality problems. In my neck of the woods I know wild grape vines can contain water and clumpy mosses can be uplifted and squeezed to drain their moisture; neither of these sources provide a lot of water, but it is good to know they're there and in areas that I see good environmental quality indicators and no bad ones (eg. no input-intensive farms nearby, various water quality indicators looking good).
Topography. Water flows downhill and accumulates in valleys and depressions. You can head downhill and you will eventually find water (even if it's the ocean!) A major challenge with this is reading the larger landscape and not getting stuck in local variations of the overall landscape. For example, to actually go downhill you may have to go up for a bit, or if you just follow the closest downhill path you may end up stuck in a higher area and not going in the actually easiest direction for lower elevation. If you have or can get a general perspective of the landscape, you are much better off! Knowing the general trends of topography and where rivers span is very valuable. A topographic map and compass are precious in this case, and even if you have neither, being familiar with the overall topography is a huge asset as it tells you what general directions you can reliably go in to find important features (roads, rivers, low spots) rather than 'shooting in the dark'. If you're in the woods and have none of that familiarity, you can try to see particularly high or low areas from openings in canopy or vantage points you can find, and go from there making best guesses about topography.
A major challenge in both of these cases is limited visibility due to forest thickness. In that case local topography can be hard to gauge and you really need some familiarity with overall topography trends beforehand. Otherwise you are much worse off, but still trying to use the guides already mentioned is better than wandering aimlessly in search.
And of course, an ounce of preparation is worth a pound of cure. Bringing a topography map can make this process way easier, and bringing enough water can make this process unnecessary. And even if you find water, you'll sure want to have at least sufficient containers (or ability to make them) if not also purification methods available.