It’s 100% this. Asking for a cut that’s super short, the hairsresser can always take more off but can’t add it back on. Either keep telling them “a little more off”, show them a picture of what you want (preferably a picture of yourself with the style from when you’ve previously had it done), or at the very least give them assurance not only that you are ok with the buzzer size you give them, but that it’s alright if it ends up shorter than expected.