I'm curious as to how people interpreted this. Does the latter mean that one believes in the supernatural but without a god figure, e.g. buddism, new age? This question looked confusing to me at first glance.

I would have expected the opposite given Yvain's definition of "supernatural". The existence of an agent (or agents) that created the universe seems much more likely than the existence of ontologically basic mental entities. After all, one man's lead software designer of the simulation is another man's god.

People who believed in high existential risk were more likely to believe in global warming, more likely to believe they had a higher IQ than average, and more likely to believe in aliens (I found that same result last time, and it puzzled me then too.)

Why does it puzzle you?

I assume because higher existential risk would seem to generalize to lower chances of aliens existing (because they had the same or similar existential risk as us).

If I remember correctly, the terms were defined in the survey itself, such that "spiritual and atheist" was something like believing in ontologically basic mental entities but not believing in a God that met that description. I didn't find the question confusing, but I did find it only peripherally related to what most people mean by either term. That said, it is a standard LW unpacking of those terms.