“His family described him as a former fighter for the militant Islamist group, but who in his older age had taken an administrative role”

…this sounds like a valid military target. Hezbollah is a terrorist organization that, bewilderingly, has declared war on Israel. Whether or not Israel should be mucking around in southern Lebanon is somewhat orthogonal to the validity of an attack on such a man. (And being able to reduce civilian casualties with a phone call is a good thing.)

Given the IDF’s record, I’d assume a more-sympathetic target could be found.