The social security net isn't paid for by the people it helps at the time they're receiving the benefits. It is designed on the principle that many of the benefits are temporary subsidies which some of the recipients are going to pay back in future out of higher taxes (or have already paid far more in their taxes for years). Obviously there's some net rich to poor transfer, but the main point is that both social security and UBI have direct costs to people who are actively buying making stuff, making stuff and investing in creating jobs in the American economy, which may or may not be greater than the economic gains from poorer people continuing to spend in downturn, not defaulting on their loans and being able to afford to sort out their health problems or relocate to somewhere with jobs, depending on how efficient the redistribution is. This, on the other hand, is just giving 6000 people money that local economy wouldn't have otherwise seen. Of course the community is likely to be better off overall, and even the rich people are going to think it's a totally brilliant idea because they're net gainers too.

Studying the effect of large scale outside cash injections into a community is not a remotely plausible proxy for studying the economic effects of a redistribution scheme.