See how your level is curved and the water is straight.
Are you claiming the camera can now curve a straight edge without curving the horizon?
If the camera curves a straight edge it will curve the horizon as well if they are in the same photo.
Maybe if you look close enough you will notice that the particular photo you are referring to the level is on a slight angle.
When you make the effort to try these little experiments it can be a little tricky setting these things up on sand.
So how about you focus on the first photo with my name in it.
Is it a good photo?