My understanding is:
1. The idea is the extra $1k allows people to pursue careers they are passionate about, even if they traditionally pay less or the pay is volatile. $1k on its own is way below poverty. Not exactly enabling people to not work at all. So, back to the question, I don't think it creates jobs overall, but it makes some careers more viable.
2. Maybe more people could afford to go to the gym, or even a personal trainer, with the extra income. Maybe a family gets stronger because they can finally afford a vacation.
3. Assuming his stance hasn't changed, part of the deal is that to qualify for the $1k you cannot be subsidized under any other government programs. So it could, in theory, get some people to stop gaming the system for disability, unemployment, etc. Which would also cover part of it's cost.
Lord knows if it'll work in practice, but I can understand the sentiment and appreciate the stuff in point 3. He commented specifically about how this was free and clear and the impact that can have mentally vs being on disability and potentially even dreading getting better because you'd lose disability. So then you almost want to be disabled, if that makes sense.