The article doesn't specify whether it's an RTG or an actual critical fission plant.

An RTG is more what I'd describe as a "battery".

I'm guessing actual fission since they seem to be dancing around the topic of how it works. It would be possible to build a sort of "solid state" fission plant with low enough core energy density such that liquid cooling is not required, which could allow a much smaller and less-complex plant.

No reason this can't work but personally it seems safer to consolidate fission generation in large plants rather than spread out through the community?