UBI (at least in all the circles I've seen) refers to basic income wherein the government gives an unconditional sum of money to citizens. Negative income tax is not unconditional.
Everyone gets the UBI, but the more money you make, the more you're paying in additional taxes to support the UBI. At some threshold you're paying as much in additional taxes as your making in UBI payments. Past another threshold and you're paying more in additional taxes than you're taking in.