Yeah... I'm sure that clown had plenty of room.
You could put things like mushrooms, zoas, various types of polyps. I mean... 1g is pretty small and a lot of the LPS get fairly large and would take up alot of space in that tank and if you put more and more lps on there.. They would definitely start to agitate eachother from the lack of space to grow out.
Same thing goes for the SPS species... But those would be a heck of a lot harder to keel in such a small tank since they need pristine water conditions to thrive. I'm sure it could be done, but you would need to keep up with that tank like it was your job.