I see this all the time. It has to do with ignorance and the carelessness to not read the label of the product and how it is to properly be administered. All of the flea and tick products in the US if administered improperly by mouth will cause problems but rarely death. There may be some intentional malice in this instance.
My own mother killed a wonderful little,well-behaved dog,”Cap’n Stubby”,by putting in his food the same dosage of worm medicine prescribed for our other dogs of five or six times his weight.He died of convulsions.And she was blaming it on snakes must have bit him,etc. until asked the right questions. Still doesn’t really admit /believe she killed him.
There are millions of people who totally ignore the actual directions and instructions of use for products ,but instead just go with how they “think” it should work.These are the people who tell themselves”if one teaspoonful is good,three will be better” ,and give cause to those who call for ever more regulation.