Judging by the size, I would say it was probably something like a rat.
One of the cool things about thermal is seeing stuff in the dark that you likely never realized was moving around. For example, I have been hugely surprised by the number of mice and rats that climb in and out of trees. Generally speaking, squirrels were the only rodent I thought much about climbing trees, but mice and rats do it all the time in the night, some in the day time, but most at night.
With night vision, I had never noticed rats and mice stealing corn from around the feeders, but with thermal, I see it fairly regularly.