Earlier quoted context omitted.
I've always liked that line, but it's clearly being cheeky and there are times it's applicable and times it's not. All arithmetic is math, but not all math is arithmetic. Except that if you dig deep enough, all math is arithmetic under the hood. Algebra is doing the arithmetic on variables before they're numbers. Calculus is just useful shorthand for compound arithmetic; the derivative is a divide and the integral is…
Actually, the opposite is true. If you dig deep enough, it turns out that arithmetic is far more complicated than most other areas.
Seems like you agree more than disagree; math and arithmetic aren't easily separable, if you're being serious instead of cheeky?