No Colloidal Silver is not toxic cats, unless it was made improperly or the water was contaminated, or the silver impure. I've given Colloidal Silver to all of my cats, many, many times. No harmful effects, in fact the opposite. Colloidal Silver eliminated their infections. I make my own colloidal silver using .9999 pure silver wire and water that I distill myself. Before that, I used Utopia Colloidal Silver so I knew I was getting a quality product.
That poor animal was obviously given something else besides colloidal silver or it was contaminated with a toxin.