The confession Garurumon hears is one he's not sure what to even do about...
"...you sure you're not getting told some random thing to see how gullible you are?"
...because he doesn't know what a solar system is either. Obviously he knows what the sun is! His world has a sun, after all! What's not for sure is if there's anything else up there beyond the skies. Probably nothing, and if there is, it sure won't be a solar system, and why would Garurumon know about what outer space in the human world is like?
So overall, Dan stating he doesn't know what a solar system makes him likely to think someone was playing a joke on this guy.
I
"...you sure you're not getting told some random thing to see how gullible you are?"
...because he doesn't know what a solar system is either. Obviously he knows what the sun is! His world has a sun, after all! What's not for sure is if there's anything else up there beyond the skies. Probably nothing, and if there is, it sure won't be a solar system, and why would Garurumon know about what outer space in the human world is like?
So overall, Dan stating he doesn't know what a solar system makes him likely to think someone was playing a joke on this guy.