Blood meal and bone meal can sometimes be interchangeable but there are marked differences. Yes, they both come from animals but as I am sure you have guessed, blood meal is derived from animal blood and bone meal is crushed up animal bone! Bone meal does not have high concentrations of nitrogen like blood meal but is a good source of phosphorous which is essential for root growth.  If you are worried that you have put too much blood meal on your garden, then you can also use bone meal to counteract this.