The author's ultimate assumption is that money supply is somehow decoupled from accumulation. People receiving money from the government and using it to buy their basic needs may not drive inflation because their labor is not being procured by anyone else AND those basic goods they are buying would not be produced otherwise. However, the constant money stream will drive accumulation on the other side of the economy.
The owners of capital (or the 1%, however you may want to call them) would become unimaginably wealthy in a scenario like this. And it would be hard to prevent that. A super wealthy class is already a big problem today. Imagine the influence that group would have in politics if they had 10x the purchase power they have today.
Another problem that I believe exists with instituting a UBI through money creation (e.g., MMT) is lack of innovation and market disruption. It essentially puts a tax on innovation. In order to hire people you now have to be able to afford to pay more than the government and still have sufficient funds to fight well-established mega corporations.