If the container wasn't in the shade, then it is highly likely the culprit.
Alafalfa is fine once cooked, but adding a lot at once will generate a lot of heat in your soil...heat you can feel with your hands and worms will be unhappy and so will your plants if you dont wait till the temps go back down.
Alfalfa is good stuff. Good source of nitrogen and it has natural growth hormones that enhance bud set, when steeped into a tea and fed to plants during the first 3 weeks flower.