when we see, we're always comparing what we see to what we've seen before & trying to recognize each thing as a shortcut to our existing understanding of that class of thing. this means that we usually don't take in all the details of everything we see, rather just enough to recognize the thing & move on to the next thing. young children are seeing things that are totally new to them all the time, but as adults it's rare that we see anything for which we have no existing reference.
as in the video, if we're on the look-out for something of interest, or a threat, then we can very easily discard much of what we're seeing to concentrate on some particular thing.
the stick in the water appearing bent is interesting because we do interpret the light hitting our eye correctly, we're not mis-interpreting what we're seeing as we are in a perspective illusion. if we can see that the stick is half-in & half-out of some water then we might take this into account & doubt the literal interpretation of what we're seeing.