I love watching how to carpet cleaning videos put out by other carpet cleaning companies. I have been a carpet cleaner in Tampa FL for several years and yes there are several different ways to remove blood from carpet, but some ways are better than others.
I would suggest that the first step in cleaning any carpet spill is to remove as much of the spill, in this case blood, with a dry towel. Blot the blood gently to remove the excess off the top part of the carpet. This will make it easier to get he rest of the spot out. I agree with the video that a solution of water and a few drops of dish washing soap should be the next step in trying to remove the blood stain. if you don't have a spray bottle you can wet a towel with the cleaning solution and blot the blood stain to get it wet, then use a dry towel to remove the blood and cleaning solution.
After removing as much blood as possible with the soap and water cleaner, there be very little red left in the carpet. I suggest skipping the ammonia and water mixture and move to the final cleaner in the video, hydrogen peroxide. However, I recommend cutting the hydrogen peroxide with more water. I suggest a 1 to 1 ratio of water to hydrogen peroxide. Trust me it will still be effective. I used this to clean blood out of my own carpet in Tampa FL.
There is no real reason to rinse with plain water at the end. If the blood has been removed from the carpet drying is all that is needed. If these remedies do not work it might be time to call a professional carpet cleaner to get the rest of the blood out.