This is what was said - the IDF is operating under the assumption that Iranian Revoultionary forces fired the missile 1) b/c Iranian special forces are in lebanon and 2) the missile is Iranian made and 3) Hizbullah denied firing it
'Under the assumption' means they don't have evidence--at least it is a serious yet somewhat toned down way of saying it. At least that is my reading. Regardless, I think even just 'assumption' is enough to prompt Israeli's into action when it comes to attacks on their land and people.