He’s not singling Israel out, but the effect on Israel would be unique. Unlike other countries, Israel relies on that aid for its very existence. Those other countries aren’t surrounded on all sides.
Another angle: Israel is the one sane country in a sea of craziness. It is democratic, it is productive, its population is pro-American. It would be cruel to cut off aid to Israel just because we cut it off to all the other sleazebag nations we send aid to. To do so would superficially be fair in the sense of being consistent, but in fact it would amount to an unfair singling out of Israel since Israel is the one nation that is worthy of our aid. Israel deserves to be dealt with according to a different rule.
I wish apologists for this aid would get their stories straight. This contradicts their usual rationalization for this welfare program e.g. "it isn't really welfare and the U.S. actually makes money from it."