Set Harth wrote:
But it seemingly destroyed the Romulan capital before coming anywhere near other planets whose destruction would have been worthy of note, such as the Klingon capital, Earth, or, say, Vulcan. This implies it most likely originated in Romulan space.
Klingon and Romulan spaces are very close to each other. Also, we don't know how this nova works, so saying it "implies" anything is speculation.