Read the genocide statute linked above, genocide just requires an attempt to destroy a protected group in whole or in part, combined with some specific acts, has nothing to do with effectiveness or number of deaths.
Hamas openly intends to destroy Jews/Israel (which, as national, ethnic, and religious groups are protected) as per their charter. Israel claims they are attempting to destroy Hamas, which is not a protected group.
Call it a massacre, call it terrible, call it any number of negative terms, but it's not genocide.