That is, if you make below a certain amount, the government gives you money until your income reaches some base level.
However, their framing leads to different expectations. For example consider a flat income tax of 25% on income less $20k (going negative below that so unemployed people get $5k credit). Raising the negative rate to 50% sounds kind of progressive, since you're giving more to poorer people, but frame it as Basic Income, and yes you're increasing the baseline from $5k to $10k, but you're also implementing a 50% regressive tax band up to $20k earned income.
Another point is that they'll tend to be implemented differently due to framing. Basic Income is likely to be part of the welfare system, and since it's unconditional, you can just register once and receive it in perpetuity. Negative Income Tax is likely part of the tax system, so to get it you potentially need to submit a tax return saying "Earnings: $0" every year, which makes it more embarrassing.
1) something like reducing that payment by $0.50 per $1 earned as an example.