Recreated the angle again in a sandbox environment on medium graphics, the black bars do become more transparent surprisingly but I'm still not convinced as to how you saw anything in the first place
Alyx model placed for reference to the approximate location of the player in the field
Angle from the same spot in the pool, Alyx is completely covered by the fog and probably 2 or 3 layers of brush
Same angle using the scope of the HL2 crossbow which is comparable to the 8x scope on a Raging Bull but again I still cannot see the model I placed
Same angle, standing up without the bar obscuring vision
I went back and placed around 10 more Alyx NPCs in different spots in the same area and I can still not see any of them through the black bar, but 3 of them would be at least faintly visible if I stood up and zoomed in.
The only other explanation I can think of for you seeing him is that your bushes didn't render so his model was contrasting clearly with the fog at that distance, but that doesn't explain why you sprayed the bushes after seeming to know where he was for the first couple of shots. As for aiming around the corner, I understand that a skilled FPS player would keep their crosshair along the edge of the corner after seeing someone run by, but what you did was move your crosshair past the corner, stick it to the player's model until you rounded the corner, and then attempted to shoot him.