Yeah it's def an island with Radz-at-Han as the capital. The OP of this thread has the sources listed already if you want to see for yourself (most relevent the item descriptions for Adamantoise Shell and Thavnairian Mistletoe). Mint Lassi does refer to it as "city-state" though, so there may be a conflation of terms here. What is 100% clear though is that it's definitely separate from Othard.