Israel is a sovereign nation, the Houthis are not.
Under international law, the attacks of a nation are the responsibility of the attacking nation. The same is not true for independent militant groups. For example:
France arms Ukraine and Ukraine attacks Russia, Ukraine is responsible. Iran arms Houthis and Houthis attack Israel, Iran is responsible.
Israel is a sovereign nation, the Houthis are not.
Under international law, the attacks of a nation are the responsibility of the attacking nation. The same is not true for independent militant groups. For example:
France arms Ukraine and Ukraine attacks Russia, Ukraine is responsible. Iran arms Houthis and Houthis attack Israel, Iran is responsible.