It's a lot more than a hunch, it's standard economic principles. The standard sources of inflation are money supply increases and supply crunches. The OP specified a UBI that doesn't increase the money supply. Nor would UBI cause a supply crunch. So why would you expect inflation?

> OP specified a UBI that doesn't increase the money supply. Nor would UBI cause a supply crunch

These are assumptions. I’m sceptical of both, but think an experiment at the state or small-country level is worth a try.

Not increasing the money supply isn't an assumption, it's a choice.

> Not increasing the money supply isn't an assumption, it's a choice

Then it works at the state or local level. My point is in interrogating the reason state and local experiments don’t scale to a national example.