I just saw a pretty awesome video.
Now, to do an actual scientific study, you'd probably want to do a lot larger study, with different flow rates and different types of blood...but this one ain't half bad for a YouTube video.
It's important to remember that just because something told you something is true doesn't mean that they're not a bloody liar.
Science is the use of scientific methods to determine the truth of various things in reality. You try to eliminate as many variables as possible to determine if something is true, or if something has a correlation, or something like that.
Now, the guy in the video didn't really prove much...other than perhaps that a study should be done on perhaps what different types of sharks may be attracted to different types of blood. Clearly they weren't that interested in the amount of mixed human blood that his machine was pumping out, but would they perhaps have been more interested if the amount of blood was a bit faster? Are they not attracted to human blood much at all? Would they be interested in different types of human blood? Would different types of sharks be more interested? Would they be more interested in the blood of different animals, such as seals?
I think that he perhaps did bust the myth that sharks can smell a drop of blood in the water, but clearly they seemed to have some interest in cow's blood, at least at the rate that he was pumping it, though it did seem to take a while for them to get interested. So, if you're bleeding to death in the middle of the ocean, maybe a shark might be interested, if you're a cow.
There are a lot of myths that are spread by people all the time. Maybe the next time you hear something that sounds a little fishy, do a little research, and see if you can find any info on an actual scientific study on it. Scientist go through a lot of effort to eliminate as many variables as possible to find the truth in reality. That's important.
Especially if you're stuck in the middle of the ocean, bleeding, and surviving might actually rely on you not panicking because you think some shark is going to come and eat you. So, stay calm, and remember, sharks probably aren't really even that interested in you.